This shows that Sigma USA Service can indeed fix the wide-end wide-open front-focusing on the 20D by doing their "Replaced flexboard and adjusted element" fix.

These are 100% center crops (with full height) of photos I shot in Av mode at f/2.8. Here's the order:

24mm before repair (shows severe front focusing)
24mm after repair (shows no front focusing)
70mm before repair (shows no obvious front focusing)
70mm after repair (shows no front focusing)

All shots were taken inside from at ISO 100, on a tripod, with MLU, using a 20D in Parameter 2 mode, best JPEG mode (not RAW), and with center AF point on the middle of the orange X (about 6 feet away). No post-processing whatsoever other than cropping.

Please excuse the differing lighting conditions:
Before repair: incandescent lights, some window daylight, and the 20D's internal flash.
After repair: incandescent lights, some window daylight.