Can u Crossfire ATI Radeon 4670 with ATI Radeon 4850?

No.

The architecture is different.

Actually you can crossfire ATI different card models together but you cannot SLI NVIDIA different card models. All models of HD 4800 series has the same R700 architecture. This is one capability of Crossfire that SLI does not have. However I would never recommend you to crossfire 2 different card models because you risk to bottleneck the speed of the faster card. In other words, Radeon HD 4670 could bottleneck/lower the speed of Radeon HD 4850. The faster card's speed would be lowered to the slower card's speed so it would be a waist of money to get Radeon HD 4850. It is better if you either crossfire 2x Radeon HD 4850 or 2x Radeon HD 4670.

^^^

Hmmm... Really? I didn't know ATI cards progressed that far where you could use XFire different models.

If that's the case then the 4850 would slow down to the speed of a 4670, thus it would probably be the equivalent of two 4670s XFired.

Either simply buy the 4850 or step up to 4870 if you are looking for a single card solution. Otherwise simply drop in another 4670. What's the performance gonna be like? I don't know, never seen benchmarks of 4670 XFired.

Probably a little faster than a 4850, but don't make your purchase simply on my guess.

Wait, you're trying to say you can Xfire an HD4670 with an HD4870?

That's not right.

HD4830 and HD4870 fine, but not 4800+4600. Shader # TMU # ROP # don't comes close to matching up.

Here's an easy to view chart;
http://game.amd.com/us-en/content/ [...] _Nov08.jpg

The pairing is correct though, and they will adjust to match the lower of the two cards, see the FAQ;
http://ati.amd.com/technology/crossfire/faq.html

Just sell the old HD4600 card and buy the HD4850 if you want, heck take the savings from selling the HD4670 and get a 1GB model 4850 or even a 4870, that would be better than trying to run them in tandem.