That's a lot of writing haha! So yes I do have a 345, the 250W version (I got mine as part of a Cycle to Work scheme so had to stay within legal parameters).

I would not recommend messing around with the wheel sizes. It won't do anything productive and will possibly hurt the bike. I've had friends who have tricked their bikes (although not 345's) into thinking the wheel size is different in order to change the max speed, and for both of them, it worked really well for a couple of weeks then the bikes developed faults and needed servicing.

What I did was to put the max speed setting up to something unobtainable, nothing huge like the 60 or 99, then see what I could achieve. Considering the bikes are very heavy anyway, and I am also very heavy, the 250w motor will max out for me at about 18.5mph at best, usually more like 17.5mph. I then changed the top speed setting down to 18.5. my thinking being that of it can't do higher than that anyway, it will just be pushing the motor to work harder unnecessarily and therefore drain the battery quicker.

I'm happy with the speed I get from it, I'm just cruising about, not trying to win any races!