New Canon Question

Up until just a few moments ago, I had decided to purchase a new Canon EOS Rebel XSi. Now I am rethinking. I am new to the DSLR world, but wondering if I should move up the to the 40D. I like the 6.5 FPS on the 40D for action, and wondering if the the MP 12 vs 10 makes much of a difference. I am going with the Canon's due to the fact that I have access to lens. I am going to complete some further research and talk to some folks at the camera shops but thought I would ask you guys. Rebel XSi or the 40D?