Hi Jon,
These kite differ considerably. The Crossbow is a bow kite so will have considerably more power than a 11m "C" kite like the impact. You will be able to ride the 11m Impact in stronger winds that the 12m Crossbow.

The Impact will be 200% lighter on the bar than the CB and turn much faster. The turning speed is thought to be an issue for learners but we had one guy here learn on one and because it was the only kite he knew wasn't aware other kites turn slower!

Maybe ask some local kiters what they think, preferably one who kites in a style that you intend to aim for.

Jason
www.briskites.com.au/