I favour Shimano R600 (and Dura-Ace 7402 on the fancy bike) but then I don't have the biggest hands, and I prefer the smaller shape.
I think it's best to mentioned that I find the R400 to be rather flexy which from the sound of your experience, the R600 is a much better quality levers.
I think it's best to mentioned that I find the R400 to be rather flexy which from the sound of your experience, the R600 is a much better quality levers.