Mike,
Your setup might have improved torque at that speed so it would pull in top better?. It must breath more efficiently I would guess?. I'll find a suitable bit of road next time i'm out on it, which might be next year!. We always have a wind here too, so it would be good to try on a more still day.
I would think the only way to know for sure would be to ride them back to back, do you know anyone in your (large) neck of the woods who has a 350?. One of the lads on the forum said there wasn't a huge difference in perceived riding performance between the 350 and the 500?.
My great unknown is actually what the performance should be, or feel like, there are so few around, especially 350's, it would be almost impossible to ride with anyone who has the same bike to compare.
Alan.