I never believed 90s grass was faster than now. And rightly so after I read this study. I have on DVD lots of matches from 90s and 00s and they look more or less the same to me in terms of ball bounce/speed.
Wimbledon in the 90s definitely had a lower bounce, head groundsman has said as much. Not so much because of the grass change, but they roll the earth much harder than before (to make sure the grass lasts two weeks).