I wear 661 filters. Brilliantly comfy shoe. If you go go through a puddle though they will let a bit of water in but my sealskinz sort that problem out.
Damo
My mate has the 661 filters and hates them :/ says they are hard and rub at his feet too much! I have MP66 and love them.
If you were willing to spend a bit more, the 5:10 Minnaar shoes would kill all others in the running!