Well since my speedo reads 85 @ 3800 upm in 5th and I know it's not 85 because the wheels are 14's and I'm assuming it's calibrated for 15's I'd probably break 20 going 3300? @70. With 15's, 19.8 @ 85 and 3800 would be pretty good? I'm not taking into account the exta aero drag so we could call it maybe 19, 18.5?
This is a great thread for webers
http://forums.pelicanparts.com/showthread.php?t=239742