1) What do you want it for?
if the answer to the first question is "just because i can" or "for the hell of it", add question number 2:
2) Are you rich? :P
I found out I don't need anything bigger than my 030 for my Amiga needs (actually I could use an 060 for fastish demos
). if for the hell of it check out woody's link and max it all out and spend a shitload of cash for a computer that will in no way perform just as fast as a current pc/mac and has 1% (if that at all) of the software support the pc or mac platforms have.
Nothing beats the real thing but a PPC Amiga is IMO a waste of cash if you already have a platform you are content with and has all you need. If your computer needs are pretty basic and standard you can use perfectly an Amiga and it will do its job very very well.
For the TFT, you better get a Scandoubler. This is more recommended than getting an old Amiga monitor that will die in days after you purchase it or, with luck, will last you 2 or 4 years, not more.
BTW moved the post to New to amiga/emu scene because you are a newbie in anything related current Amiga (mostly like me