I had Canon 40D with 17-85. It has 9 X Sensors while D90 has 1 X sensor in the middle. If you are to shoot moving objects, 40D will be better for sure. The only issue with 40D is that its high ISO is limited at 3200 (your D90 at 6400) and higher ISOs are cleaner on D90 than on 40D. If majority of your shooting is ISO800 or below, you won't see a difference.