Without a doubt get the BFG. It has a 370mhz core compared to the norm 350mhz core, but the best part about it... LIFETIME WARRANTY!!! I purchased mine at Best Buy about two weeks ago and I think that it is the best video card purchase I have ever made without a doubt. It is a tad bit more expensive than other brands of the same card, but for an extra 30 or 40 bux I feel real secure knowing that if something happens to the card I get a new one, HA BEAT THAT! Best Buy carries the dual fan version of the BFG which I have been told runs a little hotter than the single fan version, but even after heavy gaming my card temps are about 68-69c which is in the normal temp range so no worries at all.
<i> If the creator of the human body is "The Ultimate Engineer", why did he put a recreation site right next to a waste treatment area? </i>
BFG has a better warranty (eVGAs is a 1 year). I do not believe BFG's covers damage from OCing over what they ship though.
I have an eVGA. My case has inadequate air flow when closed up, but my eVGA was running with a heavy load with an open case side at high 60's low 70's OCed at Ultra levels, and at mid/low sixties at stock. It ran in low 50's when not under heavy use. It seems, in general, a lot of eVGAs can go above Ultra levels (mine will go 420MHz Core and 1.14MHz Memroy stably, though I am running at stock because nothing is pushing it at all yet).
I *think* the BFG has 2 fans, but could be mistaken. I wanted a BFG but they were not available when I purchased. I got the eVGA based on other people's experiences with it and so far I have been VERY happy.
Either way you win I think. The 6800GT is a nice card and gives a nice bump over my 9700np. Ran the D3 demo last night at over 60FPS at 1600x1200 with High settings (P4 2.533 OCed 2.85, 1024MB DDR400), so it can even make a nice mid level system perform very well.