Where can I find AW14500 with 900 mah capacity? all I can find are 14500 (750mah) and 17670 (1600mah). With that I should get more than double the runtime correct?
Check AW's thread in the market place. Not sure about 900mAh 14500, I have 750mAh ones, which run with the exact same specs as RCR123's at 750mAh.
If you mean more than double the runtime from 750mAh to 1600mAh, then yes.
How much runtime do you get on turbo with this setup? if the cells won't fit, will I be able to just sand down the battery tube to make them fit without compromising the tube?
You could always sand down the inside of the tube - or have it machined. If we're talking about thousands of an inch, it wouldn't compromise anything, but I know you'll have some fun cursing while doing that. The tolerance on cell size are usually tight enough, so I wouldn't worry too much. Worst case scenario, you'll have to remove both the head and the tailcap to push the cell out when changing it.