Well, there's good news and there's
bad not so good news.
I received the DNP freewheel yesterday and went about fitting it last night and immediately ran in to problems. As
@RossG mentioned, the gears on the DNP freewheel sit further outboard than on the Shimano that was previously fitted. This is great for giving clearance between the derailleur and the hub motor, which was previously a minor issue, but it comes at a price...
When I torqued the axle bolts up, everything locked solid. The gear train could not be moved at all. A quick investigation revealed that the 11t gear on the DNP now sits beyond the shoulder on the 14mm axle that normally sits against the dropout! The good news is that moving one of the special fit washers that came with the hub motor from the outside of the dropout to the inside cured this problem as it's just small enough on the O.D. to fit inside the freewheel open end and bridge the gap from the shoulder on the axle to the dropout. However, I am keeping a close eye on it as the washer deformed slightly once the axle was torqued up.
The rear derailleur needed setting up again due to the different spacing but that was quick enough and indexing is spot on.
Unfortunately during repeated wheel on, wheel off, I chipped half the friction material off one of the rear pads in my new brakes
. New pads arriving today, along with a much needed BB replacement.
Anyway, the ride into work this morning was much better. Instead of spinning out at 16-18mph, I could sustain a 20-22mph cruise, no problem. I actually spent more time on the 13T cog which offered a decent improvement over the previous 14T, only dropping onto the 11T at 20+mph. There's some very minor ticking in the drive train, probably because I've stuck with the old chain, but it's only a few hundred miles old so should bed in, it did get quieter over the 11 mile ride this morning.
So, fingers crossed, if nothing falls apart, I think I now have my final setup. I've reduced the max power of the controller which is much more user friendly than before giving me from 150W on PAS 1 to circa 1500W on PAS 5.
P.S. The Halfords freewheel tool is deep enough to engage with 99% of the DNP spline depth.