Your kitted E-50 needs work then.
Motobecane's with the 30mph cylinder will go 35-40 with the stock 54 tooth sprocket. Most bikes i've seen that have dropped their rear sprocket have terrible low end until they hit about 25mph, or start going downhill.
Tim, your variator opens based on engine speed, not "resistance." raising your gearing will just give you less rpms and less power to work with at any given speed, unless you re-weight your variator.