4870X2 with a HD4850?

Hey, currently im running two HD4850s in crossfire. my specs are:

Q6600 G0 OC'd to 3.01 GHZ
4 gigs of DDR2 Ram
vista 32 bit
500 gig hard drive

and of course, the two HD4850s.

Will i need to replace the 4850s with the 4870x2 later? or just take one out and do a kind of hybrid crossfire with a 4870X2 and a 4850? will i get more performance or less? will there be a bottleneck in my system? will the fanfix work the the 4870X2?

please try to answer them all, since the 4870X2 looks like a true beast.

thanks.

It will work, but there may be a bottleneck using those two cards together.