some additional information that may help.
When reassembling the carb, I forgot which needle settling it had been on so reset it in the middle slot (3rd down), recommended being second down (slightly leaner). Plugs are dark sooty rather than brown soot, so the needle could drop a bit.
When riding yesterday, I pushed her up to 60mph but this seemed to be the limit. Prior to piston change she would do 70mph with plenty left.
The restricted to end and need to lean the mixture seem contradictory (I would have thought higher speed requires more fuel).
This leaves me thinking that the sluggishness at the moment is just a tight engine (despite large clearances) and new valvesand rods settling in.