I guess for what you running there , you should buy the Mac Desktop Pro.
I have my iMac COre 2 Duo, 17", from 2006 and I run on it LR3, PS5, Aperture 3, EOS Utility, Firefox, Safari, Chrome, Microsoft Office 2008, scanner, printer, video calls, movies etc
But never crashed (oh actually once or twice because of the World of Warcraft, but after an update everything was fine) because of system malfunction or hdd errors.

I don't know what to say. I'm sorry for your Mac experience.