Bryan, the enduro series i think is similar to the Mercury Bigfoot etc basically a stronger lower unit (gears etc) possibly a different gear ratio.
starting point is to let us know what your current diameter and pitch is, and what speed you are getting. Also do you notice that there doesn't seem to be a change in rpm between say 2/3 throttle and full, or 1/2 and full etc.
I played around abit with my 9.8 4 stroke as I was getting nothing past 1/2 throttle and now I'm good up to around 3/4 maybe a tad less. I didn't want to sacrifice too much pitch just to get the max rpm's but then again that is what is recommended.
if you want, we could go halves on a tiny tach -
http://www.tinytach.com/tinytach/gasoline.phphopfully we both need the same unit, if not maybe we can share on shipping as the units themselves are not very expensive.
Then we can measure rpms under different loads etc and you'll know where you need to go prop wise.