I've got an Intel Duo Core 6400 with 2Gb or RAM which runs very quickly.  I've been really impressed with the render times I've been getting (although the only thing I've got to compare it to was my old AMD 2.4GHz with 1 Gb RAM).  Bryce 6 (and 6.1) definitely maxes out both cores and takes a pretty fair chunk of the RAM too.

If you have a couple of test renders (preferably something that isn't going to take toooooo long to render) drop me an email with them on it and I'll tell you how long it takes to render on my box.