Contrary to popular beleif - so much of effective shot making depends on the racquets-swing-weight.
No federer will be more effective with a 88-sq-inch head-size & maybe 10grams more weight added. His 90-inch Prostaff is basically a 93-sq-inch headsized racquet because of how wilson measure headsizes, He'd be more helped by a more Prestige-Like headsize (88/89.5 s inch ) - so it'll swing faster through air & 10-grams more weight ( so that his hits will be heavier ) - so that Fed can end rallies early with winners instead of rallying for hours & losing to pushers.
with a smaller--heavier-deadlier racquet Fed can pull the trigger in long rallies early & win his way, remember getting more aggressive w/his second serve & going nuts on attacking the net made Sampras deadly in later rounds during his later years, Fed is not gonna do S&V , but he can certainly end rallies faster rather than strething it - which never favours him. I KNOW IT WILL BE VERY RISKY , but c'mon - it's God.Fed we are talking about - if anyone can pull it through - it's him. Also think about the joy it'll bring to spectators - Fed going for his shots ...... he always looks better when playing aggressive.
This is why I advocate Federer going back to his PS 6.0 85.