Probably not in general, but you can tell by running some cpu, gpu, and fps monitoring software. If your cpu usage is maxed, but your gpu usage isn't, it means your cpu is the limiting factor. But if you're getting playable frames, it's not a big deal. You're always going to have one part "bottlenecking" another (i.e. being the limiting factor to more performance), but I think that term is thrown around way too much. BF3 is going to like a fast cpu probably more than some other games, but you'd maybe see a few extra fps from upgrading, since you already have a quad core. If you're going to upgrade, i5-2500k is an excellent buy, but if you were planning on holding out for an ivy bridge anyway, you might as well wait.