Imagine3DThat's the central repository for any Imagine stuff besides 'ol Aminet of course.
A 68040 will most certainly give you a speed boost. A 68060 is even better.
I'm mixed on using Imagine for Amiga and Imagine for Windows. The two are practically alike, but Amiga is sadly lacking when it comes to render speed. Even the 68060 looks slow compared to even a Pentium 3 (which I use) when it comes to rendering. I find myself getting frustrated with the slowness when I have a fast PC that can give you instantaneous results. I have limited time and can't wait the hours it takes to do renders.
