I have a mac pro 8 core with 48 gb of ram and I just picked up The Witcher on steam. There is no reason it should chug, I edit 4k hd video on it all day, no problems. Any ideas?
Yep depends on the GPU. If you are using an older Nvidia GT120 or ATI HD2600 XT that shipped with some mac pro's well there is your problem..
I just played through Witcher 2 on my MPro 2.8 2xQuad 2008 with 16GB ram and a ATI 5870 and was able to run at high settings (with some at Ultra) at 1920x1080 no problem at all.
Witcher 1 enhanced edition run's maxed out at 2560x1440