Xenon27 made a great post on this a while back,
also wattage should not be directly linked when deciding on a drivetrain speed. weight has a huge role in this desision as well as your gonna wanna maintain decent acceleration and reduce burn out. for example a 10 pound 44w robot can run a speed alot faster than a 40pound 66w robot (obviousley a little exagerated) but there is kinda some common ranges you should fall into.
for 66w which iahve the most expirience with this is the rules i follow:
0-12pounds (ideal faster so between 75 - 86 ip/s)
12-15 pounds (68-77) in/s
15-22 (60-68 in/2)
25+ (realistically consider a readesign cuz this is really fat but dont run faster than 65in/s unless your doing crazy 8m pto transmisison shenaingans)