I've been a grip #3 (4-3/8") lifer. From growing up w/ the Agassi Radicals to the current gen Speed and PA98. Never had an extended period w/ anything smaller. I demoed the PA98 in both #2 and #3, but didn't find any significant difference in my playing experience.
However, for the past 2 months, I've been playing w/ the GT98 pre-release, and it's in grip #2. The biggest thing I noticed was how much looser my wrist and grip were through contact. It's most obvious on high, heavy balls.
I've been thinking about entertaining playing w/ the PA98 at grip #2, but the idea of selling my PAs and re-buying them at a smaller grip size seems exhausting.