wow, you're right, I never even looked at those points. Even when I owned a 1 series I basically use center, top, bottom, left and right. But I've also said I'd prefer this layout:
The corners are perfect for me. They're placed on or very close to the third lines, which is ideal for non-central compositions. I use the corners probably about 90% of the time, and the top and sides for most of the rest of the shots, and the centre probably around 2%. They're placed so well that it really is perfect for non-recomposing.
yeah, about that, I had a 40D along side my 5Dii for a month. The 5D I never used anything but center in low light. The 40D, I tried, it could see what it needed to do, but it's AF SPEED couldn't get there fast enough before my subject moved. The center point could. With the 5Dii, the outerpoints can sometimes see it, sometimes not (it all depends on if the contrast crosses the sensor in the correct direction). When the 5Dii sees contrast it can use it focuses faster than the 40D outerpoints in the same low light. When it can't it won't. Yes, that's frustrating and yes I wish we had all cross types, but I find the 5Dii better than my 40D was in very low light....
It depends on how low the light it. If we're talking like EV0 then yeah, the outer points can struggle on the 40D, but with an AF assist beam, the speed snaps right back up and I'm flying again. It wasn't quite so on the 5D, and the 30D/20D for that matter.
also, how do you find your D700 outer points? Especially the left/right ones that are not cross types either? I would have though they'd be lacking in low light as well?
Surprisingly, the D700 corner non-cross points work _really_ well. I know all the crosses are clustered in the centre, but the outers work so well that I could care less. But one thing I noticed is that it has an easier time locking onto different contrasts than my canons. For example, in crappy light, the D700 seems to love locking onto facial features like hair/skin transitions and faces, which is great. When it's really dark, on my canons I purposely place the AF point onto a hard contrast like someone's white shirt collar, and it does a fantastic job. But the D700 doesn't respond as well to that, which I find really strange as it's still a phase-detect system, just like canon's.
yeah, not sure how you're shooting, but I don't shoot more with my 5D -vs- my 40D or 1Dii. I shoot much much LESS and have a MUCH higher keeper rate. That's why I love the camera. Slightly slower (yet I can still shoot sports!) and more deliberate.
Your shooting style must meld well with the 5D; you have a great match there. I guess mine just doesn't. The thing is, the 1-series, D3, D700, D300, and even the 40D/50D somewhat, are *very* flexible and can handle many different styles of shooting (in an operational sense, not image quality) for many different types of shooters of various technical skill levels.