How good are the outer AF points on a 40D?

Just wondering if anyone else has ever tried this:

I was focusing on a target with only vertical lines with my T1i and I noticed that indeed the outer points wouldn't focus on them in landscape orientation, only in portrait where the lines 'became' horizontal. The center point worked. I tried it with my 40D and I found that while the top and bottom center points were good along with the center point, the 6 outer ones (3 right and 3 left) really weren't that good, didn't seem to be any better than the outer 6 on the T1i to be honest. I don't think this is anything new, just the first time I noticed it. Happened with my 24-70L and 135L lenses IIRC. On my 1D Mark II as expected the 7 cross points worked while the other 38 horizontal only points didn't but as the 7 points on that camera are near the center it didn't really tell me anything about outer points (on the Mark III and IV there are cross type points away from the center but I haven't .

Has anyone else ever actually experimented with vertical line only targets with the outer cross-type points on 40D, 50D and 7D cameras? Are they really as good as the center one? Or is my 40D in need of a trip to the Canon spa? Should I check the screen is installed correctly first?