Without pausing for a second, I'd go for the 2011 model. Hands down. No debate.
You will be getting a Core i5 processor that has twice the processing power of your current Mac. Four times the RAM you currently have plus the possibility of upgrading up to 16GB if needed. Watch Windows fly! And, being an Early 2011 model, it would probably come with Snow Leopard and save you the issues that many people have with Lion. Plus it will very likely be totally compatible with the upcoming Mountain Lion out this summer.
As for gaming, sorry to say that none of these are good for graphics-intensive games. The shared video infrastructure puts a severe dent on performance. If you were to want to game on a Mac portable, 15" is the bare minimum.