Need suggestions, buying a new computer

I want to buy a "monster" computer mostly for crunching big MARK models (imagine multistate robust design models with 10+ states and 30+ years of data -some of which can take weeks to run on flimsy dual core machines-).
I don't know much(at all) about processing/computers, but I've picked up that with the new(-ish) parallel processing capabilities in MARK, more cores = faster model runs = better.
Given that, and a budget of $3,000-$3,500, which is the best/fastest computer you would recommend? (If possible please give specifics pertaining to which processor, how much RAM, etc.).
The same computer may be used to run optimization models in Matlab (though I don't think Matlab would benefit from multiple cores... but it would benefit from having a lot of RAM? Is that true?).
Any help greatly appreciated!
Claudia
I don't know much(at all) about processing/computers, but I've picked up that with the new(-ish) parallel processing capabilities in MARK, more cores = faster model runs = better.
Given that, and a budget of $3,000-$3,500, which is the best/fastest computer you would recommend? (If possible please give specifics pertaining to which processor, how much RAM, etc.).
The same computer may be used to run optimization models in Matlab (though I don't think Matlab would benefit from multiple cores... but it would benefit from having a lot of RAM? Is that true?).
Any help greatly appreciated!
Claudia