The XL ranks right under the GT in most benchmarks, but not by much at all. The XT is on par with the GTX in most games, but overall is just a little behind.
The XL is further behind the GT than the XT is to the GTX.
I know because I've read tons of reviews on videocards before buying my GTX last week.
To use Crossfire you need a Crossfire chipset motherboard, a master card (the XL is rumored to not have a master card version in production), and a regular card. I'm not sure if that's what you were asking...were you asking about an intergrated solution? Any integrated solution is going to pale to almost any add in card.