Yeah that CPU will bottleneck any really powerful GPU setup like 670 SLI (although I'm surprised this happens at triple screen resolution...). That's probably your problem.
not true at all my Friend currently uses a FX 8150 at 4.8GHz and 3x HD 7970's with no problem in BF3 fully maxed. back to the question i highly suggest overclocking your cpu it's very easy as it's the only way to gt the most from a Bulldozer Chip
Edit: also don't expect a lot of FPS at that high of a res on Ultra