Question about adding one more 6970 for CFX

My current computer is like:
CPU: I5 750 (Can only small OC to 2.9g due to the stock cooler)
RAM: 8G
Motherboard: GIGABYTE P55-UD3R (Has one x16 PCIE and one x4 PCIE, cannot run in X8 X8)
Video Card: MSI R6970 Lighting
Harddrive used for gaming and OS: OCZ Vertex 2

I am just curious if I should add a second 6970 or maybe 6950 due to the x4 PCIE for decreased bandwidth. I am wondering how much performance I will get by adding a new one for CFX. Is there any significant bottleneck in my current build? Thanks a lot for the advice.

4x PCIe2.0 will hurt performance a bit (~5%).

The only bottleneck I see in your system is the CPU. You would want to overclock that to get the most out of any Crossfire/SLI setup.

What are you playing that the 6970 cant handle?

Games like Crysis 2, I just can't max it out in 1080p. And same as BF3, I can't open any MSAA during the game if I want max out the other settings.

I would like to futher OC my CPU, but I just can't. The temp already reaches 70c on my current frequency when playing crysis 2 for an hour. And I think INTEL does suggest not have a running temp higher than 72c on this CPU.

So my question is as the current bottleneck of CPU and PCIE x4, how much scaling I can expect when adding a new 6970 or 6950. Considering no bottleneck at all is 80% scaling, can I get 70%?

btw, I have a 1000w OCZZ1000M 80 Plus Gold PSU, so should have enough power for a new card.

Personally, I would spend $30 on a Hyper 212+ and overclock the snot out of that CPU and see where that leaves you.

No clue on exact scaling, sorry.

As far as BF3, drop back to High and do 2x MSAA and see if that works. There is VERY little difference between HIGH and VHigh.

Thanks for the advice, maybe I really should consider overclocking more of my CPU... sigh, $30 for Hyper 212 is not a pain, but removing the dried paste on CPU is...