First, what is the monitor/s resolution?
Second, if it's playing games/running software as you want it too, there's no need to upgrade.
Is that a unlocked 965 (965BE)? If so the first thing I would suggest is you look into overclocking it, it's an older chip but most current games really need a quad to run at their best and older games usually respond to higher CPU speeds.
Even if it is locked, it's still a useful gaming CPU, you'll need to aim higher for a replacement to gain any useful performance increases.
Crossfire has its own issues and a s a long standing AMD fanboy it pains me deeply to say this but: I really do n't think it's a good idea at this time.