PC processor temperatures have been getting silly for quite a while. I'd be inclined to wait for a Intel CPU core change or the AMD Hammer/Opteron (whichever is their 64-bit architecture change move). Otherwise you'll be spending significant amounts of money cooling and keeping the PC quiet, which believe me, is irritating :-)
That Amiga spec, at least for my 'primary computer' requirements needs a processor upgrade, an 060 or better would start to meet my requirements. My 040/40MHz accelerator doesn't, particularly with MP3 playback, although that's not just the CPU, but audio hardware that's the problem there.
Do you use your PC or Amiga primarily? Is there a game or set of games you desperately want to play, or is your Amiga just a machine you like to play around with occasionally?
(If I had to guess the rest of your PC spec, I'd say to get decent games performance you'd have to spend a good deal more than $300, but I don't know american prices that well. If it were 300 UKP it wouldn't be enough, IMO)
