Here is a comparison chart to show you that the difference between x8 and x16 Crossfire is a measly 2 frames. This goes for the newest of the new cards too by the way. Our cards of today aren't even advanced enough to max out x8 completely yet. I won't expect larger differences (which still won't be a big deal) between the two until about mid-2012. Cheers.
Here is the link: http://hardforum.com/showthread.php?t=1591268
The pcie 2.0 in p67 boards have bidirectional bandwidth witch allows acceleration for faster transfer rates.
E.g. x4 speeds on a P55 board will ramp up to x8 on P67. x8 on last gen boards ramps up to x16 equivilant speeds on P67. This is why the Z67 chipset is going to be fun. It will support x16 x16... With bi-direcional support.
Think of it as two hoses.. one hose is 8 inches, while the other is 16 inches.
The same amount of water is being dumped into each hose.
As the amount of water increases for both hoses, the 8 inch hose will start building up a little bit, while the 16 inch will be fine.
Now, think of the Asus p67 (I've only heard confirmed of asus having this tech) having this feature that uses the i5/i7 as a waterpump that attaches onto the 8 inch hose.
The x16 hose will still have absolutely no buildup of water
The x8 hose will have buildup, but has a waterpump to expel the water almost as fast as the x16 hose.
NOW... Over time.. there will be even more, and more water, and the hosepump for the x8 might only last one more generation before the x8 hose can't expel water NEAR as fast as the x16 hose.
For those of you who want "true" x16 x16 sli / crossfire.. Asus will be releasing their Z68 1155 chipset in Q4 2011. During this period of time, Nvidia, and AMD will be releasing their new 28nm GTX600 series (Keplar), and HD 7000 series (Southern Islands) GPU's. These gpu's will run 3 to 4 times faster than Fermi, and run much MUCH cooler.
I personally prefer running a powerful single card (tuning/overclocking). In this sense, my P67 PRO is perfect for me.Edited by H3XUS - 4/1/11 at 12:43pm