You just opened Pandora's box. It seems that most people claim 42mm, but I'm pretty sure than came from an advertisement from a company that makes 42 or 43mm deep rims. I have a feeling that it's a sliding scale, like bringing a frog in water to a slow boil. You also have to realize that the depth of the rim is not the only determining factor either.

I stopped worrying about it. I bought some 19mm deep rims for my next build. Why? Because I want to tell people I have a sub 1400g set of wheels (just so I can), and even a 100mm deep rim wouldn't make my slow @$$ win any races anyway.