You can't measure performance with BF3. Games can look crappy, yet require powerful hardware like IV. It'll really depend on how good they optimize it, in case they make a PC version.
A good i5 like the 3570(K) will be just fine for gaming. i7 CPUs have 2 MB more L3 cache and Hyper Threading, but that's not much of an advantage when it comes to gaming. I got myself an i5 3570K alongside a Thermalright Macho cooler to OC it a bit and it beats an i7 3770, which costs much more, at stock voltage when it comes to gaming. If you don't wanna OC, want i7 power & functions + the price segment of i5's top line, get the Xeon E3-1230v2. It doesn't have an iGPU integrated, but it's power/price-ratio is simply awesome. GPU wise you could've an eye on AMD's OC'd 7870s as they're about the same price as the OC'd GTX 660 and have more power. It's downside, like all AMD products, is the high power consumption.
In my eyes it is pointless to upgrade right now though. Just wait until Intel gets their Haswell CPUs out and upgrade to any of them with a new fitting board. The era of 1155 socket is ending already, so you won't be able to upgrade to anything better than the i7 3770K CPU wise in the future. And as I mentioned, in games, the i7 won't be thaaaaat much better than the good i5 ones. NV will also pop up with the 7XX series eventually, so maybe just wait, spare more money and get something great & future proof. It's kinda dumb to upgrade without knowing V's requirements anyway.