I recommend you post about what you plan to do - musically. If your just recording your four piece in your studio, well anything (practically) can do this, but if, like me, your composing using lots of heavy duty VSTs all loaded at once then you need a lot more, particularly RAM. Top orchestral composers in Hollywood and beyond, often have slaves, (using Vienna Ensemble Pro to link) but things are getting faster and more powerful all the time. I hope to stay on one machine.
The disabling tracks function works very well. I have a whole orchestra (EWQLSO, Halion orchestra & All Spectrasonics, BFD3 and a lot more here, organised into one big template. Its all disabled until I want it so it uses very little CPU or RAM. Most music uses few instruments and if you want a 70 piece string section then that's usually just one sample set, not 70 different tracks.
There are literally hundreds of tracks ready to go, but disabled and invisible, if I want a scottish bagpipe, its there ready to go, but when the template loads, there is nothing to see except a couple of tracks - an Audio track with a test for my Surround system, and a piano track to check my MIDI. The rest is hidden and taking virtually no CPU or RAM until I click a couple of buttons to activate tracks.
So, what I am saying is you might not need a big machine, there is a lot you can do to reduce loads (freezing, purging, reducing the size of headers) and a lot more besides.
The trouble usually comes when the user doesn't know how to do this
Still, get the best you can, spend some time learning how to set up specifically for music