Should I buy two 4890's in Xfire?

I'm building this rig:
AMD Phenom II X4 955 BE
MSI GD70 790 FX Motherboard
4 GB OCZ Gold 1600 Amd Edition
MSI Cyclone R4890 OC Edtion X 2 in Crossfire X
Coolermaster HAF 932 Case
Corsair 850 TX (850W)
Samsung T240 HDTV Monitor

I saw many reviews on 4890 and 4890 in crossfire. They all show that a 4890 performs better than a gtx 295 in Crossfire X. But I understand the deal with 'fps' like what is the fps that means the game will run smoothly without stumbling on any parts. A single 4890 can run all games at 35-50 fps in HD (1920 x 1080) but does dat mean the game is running without stumbling on any parts? The only games dat I saw dat the 4890 perform bad in are stormrise and crysis warhead, they show that it runs on 20-30 fps on full HD. Does dat mean its running smoothly? Is it worth buying two 4890's? because all I want is that games run really smooth without any glitches or problems of any kind. Or should I wait for the 5870 due in November? The more money I save buying this rig the better. So wat minimum fps means the game runs smoothly and what should I get?

I'd wait, at least until ATI releases the 5XXX series, or if you have the patience, until Nvidia releases its own DX11 parts, although that is still some time off (I hear maybe early December).
An alternative to the long wait is to do the build and install a 'placeholder' card
Either the HD4870 or GTX260 will play most games at high at that res without too many hiccups.

thanx guys but I still don't know what minimum fps means smooth without hiccups. and I saw another chart which shows that a single 5870 is 20% faster than a gtx 295!! if its true I'm definitely waiting for the 5870. But what will its retail price be? (hope its around $300-350)

http://www.brightsideofnews.com/ne [...] ealed.aspx
but here it says that 5870 X2 will be priced $599 and 5870 will be $350-400 and whats "XBox 3"?

Switch to a better PSU, the rest seems more than OK to me.
Just a point, the i7 tends to run hot and seems to like being overclocked, I'd suggest you add a better cooler and do some research on overclocking to get the best out of this beast you're planning
This is a very good PSU, not too expensive either, given its quality:

http://www.newegg.com/Product/Prod [...] 6817139005

Otherwise look for Corsair, OCZ, Antec, Silverstone, Pc Power and Cooling or FSP, 650Watts will be plenty for a single card, but up it to 750-800 if you plan on Crossfiring

Sorry, no idea, mate, unless someone else knows, all I can suggest is a Google session.

And I really mean it about the PSU, of all the components you should not skimp on, it is the one.

A another choice than the would be to crossfire 1gb 4870s. this is still one of the fastest setups out there. Alternately, like he said, you could just wait for the 5800 series but then the 4870s will drop in price, so you will likely still get more bang for your buck with crossfired 4870 than a 5800 card.

But what games need dx11 rite now? And wouldn't two 4890s in CF be a lot better than two 4870s in CF? Or would the performance gain be too minimal?

Most consider 30+ fps acceptable and 60+ fps to be ideal.
I'd definitely go for an i7 build if you can afford it and wait for an HD58xx card. Either of them should give extremely good performance at 1920 x 1080.

so 1 5870 would last me...........how many years of gaming?

Actually im building a sub $2000 gaming rig. with dual 24 inch monitor and razer mouse/keyboard/mousepad/headset.
Total would be around $3k.

anyways, only thing on the list to add is the new ATI 5870.
I've been waiting for over two weeks now...
now I only wish that the time goes faster. =/