I'll Be honest DM, It's all about the MotherBoard. get you one that will allow for upgrades for the future.
In the Past, Circa EAW, I was able to switch out a component almost every 2-3 months. Video Card, Memory , CPU, Sound , etc...
Of course I cannot do this anymore personaly, But that was how I did It, That and Just going Medium range. My only Problem with Macs, And I love them Personally ( since the old Apple IIc) Is that the games just don't seem to be written for them, hehe, SFC comes to mind.
Now If I where to make an Online Movie, Music etc. The mac is the way to go...
Unless It's a good old Fashioned Amiga like Scott mentioned. An Amiga with Video Toaster Rocks.
Don;t Believe me, Just ask "The Beast"
Stephen