No (noticeable) mileage difference between my RSTD and RSV (now departed).
42mpg cruising 65mph, 1up, no trailer.
From Yamaha, the weights are:
RSTD Dry Weight: 787 lb
RSV Dry Weight: 807 lb
I have to believe there is more than a 20 lb difference, perhaps 50, but no more than that.