lsm125, airbox+oil=bad

I'm 11.5 stone (73kg). Skinny but I'm 6.5 foot.
I'm mainly on tight twisty country lanes, between 30-50mph. But I spend a lot of time on long, straight, 60 - 70mph, two lane roads. I dont spend much time bumper to bumper but its necessary sometimes.
I really would appreciate a bit more top speed, but not sure if it'd be worth the lack of acceleration. And the acceleration would be good, but I'd not want to ride it if it was any slower. I really don't know though.

It seems to me you're the one who.... how to say... sets riding pace, and not, as it is in urban areas, traffic itself sets the pace.

If you get a chance, try a couple teeth bigger front sprocket or a half dozen teeth smaller rear sprocket. It may work for you.