Checked up the figures today for the Vr as mentioned earlier. It only appears to be on a JT8D-9 powered 737-200 that the Vr is higher than the V2 by about 2kts on an improved climb. For the same tempratures, etc on a JT8D-15 it is not the case. So I assume the lower thrust output on the -9 has something to do with it?