I am about to upgrade my pc and am looking for a good sized case with decent to very good cooling.

I am looking at a Gigabye X48 mobo with an Intel Quad Core Processor (45nm) at 2.66ghz and looking to overclock it to about 3+ ghz with a Noctua heatsink. I will also be running two ATI 4870's in Crossfire-

So far the Antec P190 seems to be the best value for money as there are 2 PSU's included with the case, a 650 watt and a 550 watt. I also have a fairly new BeQuiet 750 watt PSU I could replace with the 550 watt to up the wattage even more.

I have read that the Coolermaster Cosmos S, Thermaltake Armor+ and Xaser Vi have better cooling but in total would end up costing me almost twice as much as another 850-1000 watt PSU is the same price as the case itself.

Any suggestions on what to do, go for the P190 or for another case and seperate PSU, and if so, which ones?

I personally like the Antec 1200.

You can not change out one of the PSUs in the P190, you need all or none. The Noctua will almost certainly not fit in the P190 as well. Look at the PC P&C 750w, that should be plenty for that system. The PSU you have is rather lower quality, and when running a PSU close to its ratings it is crucial to have a high quality PSU, and there is none better than the PC P&C. As far as cases go, the NZXT Tempest has great cooling and is rather large for a good price. You could also buy a Cooler Master 830, which has excellent cooling, for a bargain if you do not mind refurbished:

http://cmusashop.coolermaster-usa. [...] /index.php

i can only support what TBR has said and back the Coolermaster 830 stacker, it is a palace of a case.