Will the two Ati 4850 +and 4890 Crossfire together ?

You need to use two exact same video cards to use nVidia's SLI or ATI's Crossfire.

If you already have an HD 4850, just buy another HD 4850 for Crossfire.

Also make sure that your motherboard supports Crossfire, and that your Power Supply Unit is capable of powering two 4850's simultaneously.

The 4850 can crossfire with the 4870 and 4830, but I'm not sure about the 4890. The 4890 isn't on AMD's compatibility chart yet.

you can i actually tested it my self but the performance gain aint worth buying the second 4890 since it has very little benift compared to 2 4850's

i bought the 4890 to replace my 4850 and plan to crossfire 4890 ltr

so all in all if you want to crossfire get another 4850, or get a stronger single gpu solution

It is possible to Crossfire two cards that aren't exactly the same but the problem is the getter card will drop down to the level of the least performing in speed AND memory.

So buying a more expensive card is a waste. Plus I'm not entirely sure there would be no issues.

Why are people with great computers upgrading so often? I upgrade every three years and just play the games that can run on my system and love it.

Don't forget you have to have a kick-ass CPU to keep up with a good Crossfire or SLI. Not to mention the noise and heat...