Personally, I went through this whole debate myself back earlier in '12 while I waited for the Maximus 5 line to be released. I was pretty well set on getting a 3770K + M5E (and a CaseLabs TH10 w 84mm Extended Top and Pedestal), but after seeing the disappointing overclocking on air/water due to the TIM issue (remember, this was in May/June, so delidding wasn't a "thing" yet, really), I went to Micro Center and lucked-out by getting a 3930K for $479 and a Rampage 4 Extreme for $308.95! The extra cost meant that the CaseLabs TH10 was a no-go for the time, but I found the Switch 810 and I have been incredibly pleased with it and don't foresee myself moving into a CaseLabs TH10 for at least another year (once I add a third GPU, I'll want to add more radiators and I have my Switch pretty well maxed out; plus the idea of running 4x Alphacool NeXXos UT60 560 rads + 2x 480 Monsta's along with multiple gigantic reservoirs is just toooooo tempting to pass up!).
Anyway, point is, I couldn't be happier with the decision to go with the 3930K over the 3770K, and the R4E is IMHO the absolute pinnacle of motherboards; the Extreme11 is close but its added complexity reduces its appeal to me, whereas the RIVE has absolutely everything you could ever need without a bunch of extra stuff thrown onto it that will never be used (seriously, why bother to put a half-@ssed "RAID" card integrated into the board, when a half-decent Areca/Adaptec REAL RAID Card will outperform it significantly, allow you to move the array between systems, AND provide upgradable cache and the use of a BBU for write-through/back caching....and a $50 sound card will outperform the "upgraded onboard sound"???).
Having the extra cores will help with Physics in games if they don't use PhysX, and it makes multi-tasking much more pleasurable. It's nice to be able to have a game open, Alt+Tab out of it and pull up Firefox which has 118 tabs open, make a quick sketch in GIMP, log some temps in Excel, and then go back into the game without issue. Part of that is the MASSIVE amounts of RAM supported by the X79 boards (the good ones), and I can tell you that having a RAMdisk (even a 4GB one) that is setup properly will become a "must have" after you use it
It's really quite nice to have 16GB (4x4GB) of DDR3-2200 9-10-10-27 memory AND know that I still have FOUR MORE DIMMs FREE!!
As far as running multiple GPU's, I've tried setups on both X79 (a RIVE) and Z77 (a M5E) running a 3930K @ 4.8Ghz and a 3770K @ 4.9Ghz, both with 4x GTX680 FTW 2GB's. During gameplay there is little difference, except that not once did the X79 setup stutter, stumble, or noticeably slowdown. The Z77 would occasionally stutter, and the mouse never felt quite right (it was almost like using a wireless mouse from 6-8yrs ago); also, the minimum framerate for the Z77 was lower by up to 25fps although the average was only about 5-7fps lower.