I love SKS. As everyone said from what I have seen now it seems that the P50 will only work well with a 26" wheel however I have a set of the P45 and they could easily handle almost the widest wheel you would want to run on a 700C bike (with the exception of something enormous like a Big Apple) so if you want it for 700C go with the P45 for the widest.
Here is a P50 on a 26" wheel.
Here is a P45 on a 650B wheel.
