Am I getting more than I can handle?

I am buying a 8 Core 2.8 4GB Ram (from apple, not that it matters) Mac Pro (potentially) from a friend for $2200 which appears to be a great deal. I know the new machines are coming out, but I expect apple will still have a 8 core in their line up, and I don't expect it to be cheaper than this. I need two monitors and the added Ram, but the processing power is absurd for me. It is still under applecare and has very little use.
Now for my question: (This would be to people who own this machine or have used a mac pro and can give insight) I am a day trader running Parallels and a bunch of other web based software in OSX all the time. At any given moment I could have 10-20 windows open and demand them to give me fast feedback without lagging (I have a fast connection). I do some computational software, but not very hard, and my wife wants a machine to start recording on with Logic. Would I be satisfied getting a 2.66 4-Core from a refurbished store online (expercom.com) and boosting the ram or having 8-Core processing power and less ram? Any insight would be helpful, thanks!

 

Thanks guys. Appreciated! I am going with the 8 core and planning on the upgrade of ram in the next couple months! I will update this forum with my impressions in a week or so.