I guess i'll take this challenge.
Uber : 98
OU : 83.48
UU : 69.01
RU : 76
NU : 70.7
There we go, the major tiers.
How'd I figure it all out you ask? Well I went to Smogon tiers and opened up the list for the tier I was calculating. I then added up all the base speeds, then counted the Pokemon in the tier. I divided the sum by the number of Pokemon in the respective tier. By doing so I received the average base speed of the tier.