I found one site that compares the 460 to the SLI 450:http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/36152-nvidia-geforce-gts-450-1gb-single-sli-review-17.html
Based on this, it seems like you'd get the best performance going with the 450 SLI option (of those you list), though it may be hard to find one? You won't be able to turn all the details up, but you'll be able to play in the 1080p world with decent quality. Just keep the AA and the AF turned down.
Borderlands and Just Cause 2 are very demanding, whereas L4D2 will run well on most setups and BFBC2 is moderately demanding.
One other thing to consider, depending where you shop and what's available to you, you can get two Radeon 5770s for around $200 these days.