I slapped myself for being so stupid.
The Tiny45 and 85 are in the same datasheet, aye.
I haven't played with varying the clock as ultra-speed has never been needed, other than divide by 8, so something new...

I guess I can measure the exact osc freq by pumping it out the external osc pin temporarily.

Is the HEX file in the code for a 16.5MHz clock??