I take the dive, personally. Processor speed is primarily relevant to render times, and your file size is limited by the RAM -- sort of. File size and polygon count are independent of one another. That is, you may have a 200 meg file with a relatively low polygon count (due to textures and such) and you may have a 1 MB file with a huge polygon count (metaballs and trees will do that). RAM will help deal with the files with large sizes / high polygon counts. I'm a Mac guy, and here is the rule of thumb I use (this is adapted from Photoshop, it's not completely accurate). You need in the neighborhood of 60 MB free RAM just for Bryce. That is, if your OS takes 70 MB RAM, you need 130 total to run Bryce and the OS. If you add shapes to Bryce, it will now require more memory. If physical RAM is unavailable, virtual memory will kick in, and it will start to use your hard drive in place of RAM, and you'll notice things slow way down. Though I don't know how much RAM an individual polygon or a primitve uses, what you do if Photoshop is this: 60 MB+ for the app alone + twice the file size in additional RAM (for a 200 meg file, you'll need an additional 400 MB RAM). So, we have 70 MB for the OS, 60 for the app, and for a 200 MB file, another 400 MB RAM bringing minimum RAM requirements to 530 megs. Again, I don't know how polygon count influences things, but I know that eats RAM, so this equation may need modification -- afterall, it was designed for Photoshop, and not a 3D app. But it should get you closer to a logical equation.