Sorry to rain on your day but Phenom 1 era machines are not usually compatible with Phenom 2 unless your board supports it. If the board is AM2+ then getting a phenom 2 quad isn't going to be a problem. As for the athlon 2 x3/4 it isn't the best bang for buck for an amd system. The L3 cache sometimes gives it a little boost in gaming.
Have you tried overclocking the cpu that you currently have , sometimes the overclock will give you the performance boost your looking for. Since your locked into the AM2 socket motherboard the overclock is your only option outside of getting a new motherboard.
You can get a phenom II 945 these days for <100 bucks. They are not unlocked, but can be easily overclocked to 3.3 on stock voltages, and 3.6 with a good cooler. They are hard to come by now that they are all snatched up. If you toss in another 10 bucks or so, you can get a 965BE that is unlocked: