Classic seeing Gilbert talking about him trying a full poly set-up.
Yet more spin would probably not help Federer in many situations and
it would also be less powerful (unless he changed frames or how he swung) than gut/poly combo. His balance of pace/spin is
a huge part of what makes him successful. I can see the argument for going to a bigger head size but the string combo is so good many of his peers (as well as tons of 3.5 level players on this board
) have even mimicked it.