Just so you know, Skip is abnormally small and he manages a 6.5" silent spinner fine.
And we have the duna wheels... But they're in the spares box and I hope they never need to leave it. If we were at home I'd check about removing the spindle, but I really can't remember and they're a 2.5 hour drive away at the mo (and I haven't got my car keys either today lol)
I found they're not too overly noisy if attatched to something secure, but we only used one for our russians for about 48 hours when we got them (they were about 11 weeks then).