I did in OS X and there was barely any difference because of the absolutely crap Quadro drivers for OS X. The Quadros really are just smoke and mirrors until they get better OS X drivers. I used to shy away from ATI cards but I’m so much happier with this 4870 that it’s going to take a lot to get me back to Nvidia - but I’ll be testing snow leopard with the FX 5600 to see if it’s improved.
voltageme5 - there’s a difference between buying equipment that helps you work and buying equipment to convince you that you belong in your field. Blindly dropping bills on hardware without understanding how it works is pretty bad - Quadros are the same cards but with more VRAM than gamer cards and different drivers. If the drivers aren’t tuned for an application (Cinema 4D, Mudbox, Houdini, being untuned) then you will see ZERO benefit running the Quadro version of an Nvidia chipset with similar video memory. I should post the video of my 12-million poly Mudbox model that I’m working on - It’s about 4x faster on the 4870 512 MB ($150) than a 1.5 GB Quadro FX 5600 ($2500) because of the difference in drivers. It’s not as bad in Windows but if you read above, someone confirms that since there’s no optimization for Mudbox, a Quadro is a bad choice (look at the memory bandwidth of those two cards and you’ll see why this is the case). But hey, if you’re looking for some extra shit for your sigwanking, go for it.

I’d vote for the cheaper card.