The i7's are a waste of money IMO...You could get a Phenom II X4 or X6 for a way smaller price, and still get a hell of a CPU.
don't spend 5k at one time.
Buy a 1-2k computer that is pretty good, then upgrade it over time, so that it will always be pretty good.
If you drop it all at one time then in a year you will have a pretty good computer, but will have spent much money