What power rating are your QSB 6.7s? That'll give an indication of what their rated RPM is. The QSBs are typically governed to somewhere around ~70 rpm above rated, so with a clean hull and full tanks, I'd want to see it propped so it hits the governors (and if you have a way to see the electronically reported engine load, it should be somewhere in the high 90s at that point, indicating that you're at slightly less than full power to reach governed RPM).
Based on what you're reporting, I'd bet you are at least a little overpropped.
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