5450 crossfire or 1 5750

An HD5750 definitely. The HD5450 is not a gaming card and crossfiring them isn't going to improve that situation much.
If you can afford slightly more the HD5770 is well worth the extra $15-20 it usually costs these days compared to the HD5750. This is a nice deal;
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Thats what i was leaning towards with the option of upgrading in the future 2 xfire 5750!
Thanks for replies

The 5450 has 80 SP's, the 5750 has 720.
Even with PERFECT crossfire scaling you would get 160 SP's.

I seriously think you're better off spending the extra, like ... 20 bucks ... to get a 5770. You'll be glad you did.

Forget the 5450 entirely. That's for HTPCs and media. For gaming, it is nowhere near powerful enough.

Yeah, the price on the HD5770 vs HD5750 is so close right now that it doesn't make much sense to get an HD5750. Unless that extra $15-20 is really a deal breaker for you.