I've got a PAW 15 (non-RC) in a 590g model (ie about 1.3 lb). This has comfortably more than 1:1 thrust/weight, although I don't know exactly what thrust it's putting out. It turns an APC 9x4 at about 11000.
I wouldn't really want the model any heavier than this (the wing loading is already a bit high with only 250 sq.in.)
A 3 lbs plane will be nicely powered by a .15 diesel. A 2 lbs plane will zip.
Are you sure? 3 lbs is 48 oz! I'm not really happy with a 15 in a stunter weighing more than about 20-22 oz. Maybe my engines just aren't cutting it!
I'm currently building a design for a Tiger replica, which turns a 9x4 at 12000 having just been run in. Target weight is 500g/18oz, with a wing area of 310 sq in and span of 40in. A PAW 19 would fly something like that beautifully.
see how likely it will be to make a model with a thrust to weight ratio greater than 1:1 (perhaps not too likely).
Shouldn't be a problem!