http://www.bentrideronline.com/?p=1484
Your doing fine,, I can average 18 mph but thats on a paved MUP that has no stop signs, intersections, curbs, dogs or cars to stop for XD
13 mph sounds good.
Other than the junk you carry your bike is 36 lbs just like my TE. and I'm 190 lbs
I like a cadence range of 60 to 90 rpm and also run the middle chaining up front and often stay in 6,7 and 8 out back.
I just cant pull top gear.
Pumping the big chain ring and cog # 7 is real fun,,try it.
http://sheldonbrown.com/gears/
Up front,
the little ones for up hill,
the middle for the flats,
and the biggun's for the down hill runs,, vroom vroom