18-19 mph plus "only" medium revs must require a lot of surface or prety light oil. Kinf of speed dominant.
I'd be careful with the SR2 as it's almost a skid/flip solid, fairly allergic to carrydown. Glad you're doing so well with a QZ-1, a very evern rolling ball, even if a pearl. Maybe you're better off with a TX-1, as it's also more even rolling, with a decent backend on emdium oil.
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"None are so blind as those who will not see."