Sup dude. very simple.
I just recently bought a Powercolor 4830 from newegg, and I have it on a (ASRock P45XE LGA 775 Intel P45 ATX Intel Motherboard
Tom's hardware 2008 Recommended Buy Award, which was 94.99$ from NewEgg, and its an awsome MOBO. http://www.newegg.com/Product/Product.aspx?Item=N82E16813157143
I am able to play Crysis on a 24" monitor at 1920x1200 on all High Settings with minor clipping. If I turn it on all medium, it never clips.
I am going to get a second videocard to crossfire it with, and i will either get a second 4830, or wait until the new model ATI is making comes out.
Right now you can get a Sapphire 4830 for 74.99 free shipping AR.... GREAT DEAL...http://www.newegg.com/Product/Product.aspx?Item=N82E16814102822
you will need a crossfire cable, I bought 2 from ebay
If you have a 4870 and a 4830 in crossfire, the 4870/50 will SLOW DOWN to the 4830's speed.
It really depends on what your time frame is, the new card coming out is going to be between the 4830 and 4850 speed and have DDR5 instead of DDR3. If you can.... I recommend waiting for it.