It would also depend on if the motor seems to be bogging at top speed or revving high. If bogging, the clutch may be upshifting too fast for the motor to handle so it stops accelerating once the motor cannot handle any more upshifting. The Pilot has a rev limiter so I would guess it is not over revving.
If the above is true, but you like the way the bottom is, you can change to a spring with a shorter free length and thicker wire. You would want a similar spring load at idle, but more at full shift out.
Find the spring you have now:
http://www.hoffcocomet.com/snow/springs.htm and compare to the other springs. For example, if you have a purple spring and changed to a gold, it would lower your engagment slightly (136 lbs vs. 129 lbs at 2-3/8") but allow the engine to rev more at higher speeds (296 vs. 254 at 1 1/8").
It is possible with the above change that your clutch will still not shift out anymore, but still gain top speed (this is still based on assumptions in the first paragraph). Increasing the spring load slows the shift allowing the engine to build more RPM which creates more centripital force shifting the clutch. If you end up at the same shift point at a higher RPM, you will be going faster. If your motor makes more HP at the higher RPM, it will allow for more upshifting.
The springs are not that expensive so you can try one to see what effect it has. If things get worse, go the other way. Just note what you are changing at each end and pay attention to the result.