February 14, 2012, 05:17:28 pm
If you bought a faster computer and graphics card, your renderings would look exactly the same (once Remko and Ferry have fixed the missing shadows on the iMacs, that is).
The only noticeable differences would be:
1) Speed: How smooth it's running and how fast it renders each frame.
2) Memory: How many models (polygons) and textures you can add to scenes.
If you feel that the iMac isn't fast enough for the kind of work you do, and you can't add many models to your scenes before it starts to get really slow, then you could perhaps consider upgrading.
If you're based in the UK, I can recommend PCs from Overclockers.co.uk. One of the most important things when buying a PC is to make sure that the graphics card has got the right power supply. These guys will make sure that your PC runs perfectly, and that it has the right components.
Without this, you can look forward to months of unexplained behaviour, strange glitches and artifacts etc, and constantly having to send your PC/graphics card back to the dealer

That being said, if you're coming from the blissfully silent world of Macs, brace yourself for incessant noise from fans, especially if you buy a PC with a really fast graphics card. Many PCs tend to sound like vacuum cleaners under full load, and use up to 850W (unless you carefully select very quiet components), so I think you should seriously consider if it's worth it, just for faster rendering times and scenes with more objects and textures.