From what I recall about the tests on CPU overclocking in conjunction with Battlefield 3, there was very little difference between dual cores and quad cores in general.
It MIGHT suffer a little on the 64 player maps, occasionally, as do most cpu's. What you're really looking for is something with the ability to overclock to a decent speed.
BF3 seemed to break the trend of a lot of recent games in that it didn't improve a lot with better CPU's, and even overclocking had little measurable improvements in fps. All of that said, I would be remiss not to overall recommend the i5-2500k instead, since price per performance it beats everything out there pretty handily, it's a stable overclocker for other games and futureproofing, and it's 4 cores which matters in some games now and might matter more in the near future.
That is the general impression I got from the data regarding CPU's and BF3 as it stands now.