I would like to add one minor comment to this mix regarding RAM memory and rendering. It will also depend on what kind of operating system you are using. Some OS's use RAM differantly than others. ( No doubt there are a few people who might debate the following - so be it, as the XP and RAM argument/debate has been around for some time)

If you use XP or XP Pro ( Like I do) it will only allow you to use 2 gigs of RAM for applications and all the rest of the RAM is used for background processes, OS, etc. In other words, if you use Bryce with XP Pro and you have 4 gigs of RAM, Bryce will only be able to use the first 2 gigs of this. So if using XP with Bryce, adding a bunch of extra RAM is not going to make any type of big difference.

My system is an AMD Athlon 64X2 Dual Core processor 5200+0 MHz, XP Pro  SP 3 with 4 gigs of RAM and this works just fine for my Bryce work. As when I disable all background stuff like network, firewall, AV, etc. I have 2048.00 MB RAM available for working in Bryce.  A memory check when I have everything disabled and before I start Bryce shows my RAM at 100%

Although one last late note on this - This OS RAM issue pertains to 32 bit XP and not to 64 bit OS.