Yeah, higher treadwear rating in general means longer lasting tire, but less sticky.

Oh yeah, and here are the speed rating standards:

P - 93 MPH
Q - 99 MPH
S - 112 MPH
T - 118 MPH
U - 124 MPH
H - 130 MPH
V - 149 MPH
W - 168 MPH
Y - 186 MPH
Z - 149+ MPH