Will I be GPU limited?
I current have a e7200 @ 4ghz and 4gb of ram on an ASUS P5K - pro ( p35 chipset fyi ). I'm looking at getting a 4850 as an upgrade for my 8600gt. I might place an additional 4850 in at a later date but for starters it will be a single gpu solution. My main question is will by system be severely limited by the gpu in a single card setup and if i get a second gpu will it perform well on my motherboard. I know that my second slot will only have 4x speed but will this be a limiting factor on a 4850 as i know it would be on a higher end card. Thank you in advance.
Don't even think about HD 4850 Crossfire on the P5K Pro. On P35 motherboards the second PCI-E slot is running at 4x, and it's PCI-E 1. Compare that with a P45 board, where the second card gets 8x on a PCI-E 2 slot, i.e. 4 times more bandwidth. Even on the P45 there are some bottlenecks, but they are small. On the P5K they'd be very bad. I've read an article about this, it had charts and all. Sorry, don't remember where it was. Anyway, the difference was huge.
With a single HD 4850 you'll be fine. When you add the second one, get a new motherboard. Some good ones under $120: P5Q Pro, GA-EP45-UD3P.
Also make sure you have a 550W PSU or bigger for Crossfire. There's a cheap 650TX at www.buy.com for example.