R9800 really isn't the card you want to run FEAR on.
My old AXP 3000+, 1024mb ram, r9800pro 128mb got only 20fps (1024x768) in FEAR with low-medium settings w/o AA
Looks good to me. 7900gt has very good price/performance ratio.
1. I don't see any obvious bottlenecks.
2. 8x is fine. 7900GT probably won't even use 8x's full bandwidth.
3. SLI does need a lot of power. I'd go for 600W+
4. Great memory, has good speeds and timings.
Suggestions:
a)...
1800XT is faster and more expensive. 1900GT is also a very good card for it's price.
Also a review on 1900gt/7900gt here . There's some benchmarks comparing 1900gt vs 1800xt vs 7900gt .