in the skate/bmx world the 5d has a focal length of 1.0x which would make a HUGE difference when shooting wide angle photography. for that exact reason I would get a 5d over the 40d. however the 40d has a 1.6x multiplier so your telephoto shots will be even more zoomed in. i also hear the 5d can render much larger prints clearer and smoother than the 40d in comparison.
the 5d is nearly 3-4 years old by now and I've heard of rumors of a 5d mark 2 coming out soon with 16MP DIGIC III. and a much like the 40d it will have 14-bit raw capture and a better AF system
hope this helps. i don't own either but I was starring at the two for a long time until I just bought an XTi instead.
