Most visualisations don't take advantage of the fast hardware on modern video cards, to my knowledge - the render the screen in memory and then blat it out to screen. This means that if you have a cheap video card, especially one that uses system memory or a PCI card, then writing mass frames per second will slow things down to a crawl. I've managed 800x600 at 25 fps in Geiss on a TNT 2, and I haven't tried it on my Athlon 1800 and GeForce 2 so I can't tell you exactly how much faster it is.

Does this give you a few clues?

Paul