Thanks for the compliment on my shots, that's very nice of you to say.
Well, there's no denying the 24-70 f/2.8 is a great lens but it's a somewhat different beast. I guess it comes down to what you're shooting - personally, I'd say the 17-40 f/4 is more useful for landscapes and architectural shooting since it provides a very wide angle, but then 24-70mm is okay for landscapes too (although in the case of landscapes, the f2.8 obviously isn't going to be much help). I guess if you're wanting to do a lot of portraits then the 24-70mm might be a better option.
So far, the combo is working great for me although funnily enough, I'll probably be adding the 24-70 f/2.8 into my arsenal one of these days, as it fills the gap between the 17-40mm and 70-200mm pretty much perfectly. So far, my impression of the 5Dmk3 is great although I'll only have a proper opinion after the weekend, as I have some activities planned to really put it through its paces. But my initial impressions are that it's absolutely fantastic - mind you, my previous main camera was my 7D, so it's quite a big jump up for me.