I currently shoot with my XTI - it seems to do me just fine for anything I shoot in the studio, but I feel limited by it's poor ISO performance when i'm shooting outdoors or at venue locations.
I've been itching to upgrade to a 40d or 50d - leaning towards the 50d, but cash is tight.
Is it worth trying to trade?
I have two of the XTI bodies, both with 18-55mm kit lenses, one with an ebay battery grip. Two chargers, 5 batteries etc.
I'm not sure who would be interested in such a trade, maybe someone looking for some backup bodies.
Or, is it going to be simpler to sell them off after buying my new body?

On top of that, I kind of need one of the camera's until I can get the new one 
