I would be willing to go overboard if the 2.93 Ghz makes a real difference. This is my parents money, and although they don't want to spend that much (and I don't want them to spend that much!) they said they would since this is for an educational purpose (I'm planning to be a music major and I need all the experience I can get). I have to work off the money anyway and pay them back so it would be a question of how much I need to work off, $400 vs. $600 (I have $900). If the 2.93 makes a big difference it would save me from having to buy a whole new computer in the future so I'd rather be safe than sorry if it does make a difference.
EDIT: The two I'm debating between are these: http://store.apple.com/us/product/FB419LL/A?fnode=Njc4MjQzOQ&mco=NjgwMDIxOA
http://store.apple.com/us/product/FB418LL/A?mco=MjE0NjA3MA
Hmmm the difference is pretty small and the 2.93 does have discrete graphics. If you can swing the jump the 2.93 should be noticably faster as it's almost 300Mhz faster per core.