@Bradley: Remember that optimizing requires dealing with the nuances of each involved component of a system. When it comes to Windows 7, it seems clear that the OS+Driver+Game is in a more refined equilibrium than is the case with Windows 8.1, for your specific hardware setup. Technically speaking, it isn't a three-way relationship, it is an n-way relationship between OS+Driver+Game+Video Card+Motherboard/CPU/RAM, etc. Windows uses a HAL, or hardware abstraction layer, that helps mitigate dealing with the issues different types of hardware bring to the mix, but they are still there and sometimes they can become a problem at a higher, less abstracted level. Windows 8 is still the same core as Windows 7, however it does use DirectX 11.2, and has a few other performance optimizations (that, as a gamer, you should really be drooling over...i.e. windows 8 has practically ZERO random drive access, and is much smarter about scheduling windows update checks and background downloads and other hefty crap like that to times when the computer is not in use...things that are a huge boon to the consistency of performance in games, and which you can primarily thank the low power mobile world for), which might require a few tweaks to drivers from both nVidia and AMD before a brand spankin new game like BF4 will run 100% perfectly on a majority of systems.
I play Skyrim these days, now that ENB is doing amazing things visually and thanks to a few dedicated modders in the community who have fixed a few of the really bad coding issues with the game. I've had problems with Skyrim for many months, even before I upgraded to Windows 8. The most recent WHQL driver release from nVidia changed something, and along with a couple bug fix mods for the games code, my freezing issues have largely been resolved. If I drop back to the older driver I was using with Windows 7 and when I first upgraded to Windows 8, many of those issues return.
There certainly appears that your issue is an issue for many players, but in reality you can rarely point to one single component of a complex system and simply say: That's the culprit! Every system is a convolution of the factors of each participating component. Windows 8 certainly plays a role...whether that role is due to DirectX 11.1/2 or something else doesn't really matter. The key thing is that Windows 8.1 is not the sole cause of the problem. The game and the driver play a role as well.
As far as recommendations go... Personally (and yes, this is anecdotal, but here you go), every time I've used an AMD card (admittedly, I haven't in a while), I had long term issues, particularly with new games. It was the same way with ATI. I can't say whether it was simply my hardware choices (maybe I just wasn't pairing my video cards with compatible motherboards), or literally due to potentially poor quality drivers, however I have found that I have far better luck, better stability and performance, using nVidia hardware. I'm first to admit that nVidia cards are not always the fastest on earth...but after having so many problems in the past with ATI, raw unmitigated performance has taken a far back seat to stability and reliability. I've used nothing but nVidia cards for a number of years now, specifically EVGA cards, and I have zero complaints. That doesn't mean swapping out your AMD card for an nVidia card is the solution to your problem...just something to think about...it MAY be A solution, or a part of the solution. So far, a 570 and an SLI pair of 760's have both worked flawlessly in Windows 8 and 8.1.
That said, I've never heard of Powercolor video cards (assuming the X79 system in your signature is the one that is causing you problems.) In reading the few reviews of their cards I could find, it sounds like they are explicitly a "cheap" brand, aiming to offer decent features at rock bottom prices. Their web site also certainly seems to reflect this...very basic and bare bones. They certainly seem to perform well, but any savings in cost has to come from somewhere. In the case of manufactured hardware, cost savings has to come from cheaper parts and cheaper electronic components. As such, all I can say is I wouldn't rule out your video card as a component in the system, so you really have a 4-way system with not three but six different relationships (OS/Game, OS/Driver, OS/Card, Game/Driver, Game/Card, Driver/Card), all of which have to be factored into any question of stability. If the card does play a role in the stability of the system, you might try underclocking it in Windows 8 by a small amount, and increase the underclock until any stability issues are resolved.
In your case, I honestly cannot say whether the issue is literally "stability", given that it is a v-sync issue. That said, I'm curious how a v-synced game could actually run at 40fps. For any standard screen, the only two v-synced options are 30fps and 60fps, as if you start missing the first sync option, you have to fall back to the next. If you have a newer screen, say one that does 144Hz, then I could see 48fps being a vsync option, along with 36fps, 72fps and 144fps...but I would expect the sync to remain at (or very near...47.9/49.1) 48fps specifically rather than 40fps or 50fps. If you are indeed getting 40fps on a 60Hz screen, then I would make doubly sure that vsync is actually operating correctly. Again, I know nVidia cards pretty well these days, but not AMD cards. In the nVidia world, from a driver vsync standpoint, you can either simply turn it on, or force 1/2, 1/3, or 1/4 frame sync. On a 60hz screen that would be 60fps, 30fps, 20fps, and 15fps respectively, and on a 144Hz screen, that would be 144fps, 72fps, 48fps, and 36fps. It may be that AMD handles vsync in an entirely different way, so my analysis here could be wrong. Anyway, I'd check into what the possibilities are. If the game does run under DX11.2, it is possible that unoptimized (or less than ideally optimized) changes to that version of DirectX relative to DX11.0 in Windows 7 are causing some lag in performance...if you cannot sustain 60fps with vsync enabled, it will usually drop to the next lowest possible tier, and perhaps AMD's vsync functionality allows something in the 40fps range.
Well, thats about all I have to offer at the moment. I suspect this has turned into a big wall of text, so I'll stop here. Regardless, while I am sure that Windows 8, DX11.1/2, and probably less than perfect drivers for Windows 8.x all play a role, all I can say is I wouldn't fear that the issue will never be resolved. The issue will surely be resolved at some point, especially if multiple gamers are experiencing the problem. Microsoft has committed to a much tighter release cycle for Windows 8.x and beyond. It seems they are willing to offer upgrades to new minor versions for free, to a certain degree...so I wouldn't worry that DX11.1/2 will remain unoptimized for long. (And they could just as easily get an update via windows update at any point between now and Windows 8.2).