disclaimer: mine was front focusing so i sent it back had it recalibrated and its now all good, only requuires a small micro adjust on my cameras now
OP has a 40D, no AFMA (but no guarantee that a Canon 85/1.8 would be a perfect match, either).
yeah but what I discovered talking to the camera tech is that they can just keep tweeking the programing of the lenses internal AF software to make it match so you could send the body in with the lens for sigma to calibrate. Inconvenient yep but for the money its a stunning lens. I think my lens was away for about a week and a half the store sent it back twice because when they tested it they weren't happy.
One thing i will say is if you buy a sigma lens get it from a store that has good service because its a bit of lottery with regard to QC of the gear. Would I make the same purchase decision again? absolutely! if the f1.2L had better focus speed and didnt have that fly by wire manual focus i may have gone for it even though its like strapping a grapefruit to the front of your camera. It certainly looks impressive and at f1.2 it is extremely impressive definately sharper than the sigma is at 1.4. I tend to keep the sigma at f2 unless i really want to get super shallow DOF also at 1.4 the sigma has some colour fringing but lightroom takes this out automatically so its not really an issue but there is a noticable increase in sharpness with the extra stop down to f2