FB DIMMS really aren't anything to be "afraid" of. They're cheap enough now, plus, if you can run in quad channel, the bandwidth is enough to feed the chips the data they need.

Certainly it's not as fast DDR2, but then again, it doesn't have to be, everything is relative.

Synthetic benchmarks show a difference, but real world usage is not affected much at all.

As for quad SLI, you do not need all four cards to be "linked" by an SLI bridge.

In fact, you never had to, the SLI bridge has been shown to increase performance by a small amount, but past that is fairly useless and certainly not necessary.