Ok..well the reason your getting piss poor performance is the prop isnt suited for your motor...at least not at the moment. 8600rpms on an 8 pitch only gives you a MAX of 65mph. With drag factored in, your probably only seeing 55-60.

Drop down to a 17" diameter and use a 10 pitch. I did that on a 80" H9 P-51 150 size that was using an 18x8 on a saito 220 and it flew like a dog. Once the 17x10 was on it, it did much better.

Even if you get slightly less rpms..say 8400 on a 17x10.....your max speed will be 79mph. This is quite a bit of a difference.

Also, if you can get a prop with wider blades, they do better at producing thrust.

I use turnigy cherry type E props even on glow or gas motors.
take a look at this prop...its only $5 but far surpasses most other props for thrust:

http://www.hobbyking.com/hobbyking/s...propeller.html

Ive got a number of these types of props on large electrics, large glow and even a 50cc gas motor(20x10)

In comparison to an MAS, Xoar, etc, these turnigy cherry wood props put out usually 25-40% more thrust, but are also light so rpms are pretty good even with fat paddle blades.

An example.....on an electric e-flite160 motor installed in my CMP me-109......18x12 APC and an 18x12 turnigy cherry wood.......I get the same speed on the cherry wood prop at 2/3 throttle as I do on full throttle with the APC. Same as with an MAS.
I can also run a 20x10 turnigy cherry wood on that same motor for more thrust(slightly lower top speed, but longer flight time)

Give the prop a shot...its cheap, but it works wonders.