At an Idle, on my i5 2500k quad core, typing away in this with various stuff open, I am using 1-3% CPU at various points.
Open up sins, start a random huge, set myself to AI, and jack it up to 8x speed, and usage jumps across all four cores.
Only one core will count much in regards to how much CPU lag you get, but it most definitely utilizes the other cores graphical processing. A dual 2.2Ghz processor is very light, if it's a Nehalem or Sandybridge, you're looking at similar performance to an old 3Ghz processor, but it's not fast. If that quad is even lower, then you should definitely go with the dual, neither of them are a prime choice for Sins though, not any better than a mid 3's P4 several years old.