I am completely confident you will have no problems playing BF3 at those settings at that RES with the setup you proposed. The 955 is a very capable processor despite its age. You will be very happy with that setup. You will have a very balanced PC and there will be no cpu bottleneck with a 560.
on a side note you do know you can OC that phenom right?? Bump her up to 3.8 ghz and you're in business my friend. you likely won't even have to touch the voltages. Just up the multiplier within the Bios or AMD overdrive an sail away. HAVE FUN
Alright, thanks. I'll be sure to overclock it a little bit. You have made my computer building experience a little easier, now I don't have to keep watching videos and comparing cpus and stuff all the time... Thanks!