Finally got this t-rex up and running so I thought I'd list a few observations, FWIW.
With the 12T pinion and 335 mm blades the head speed is nearly 2800 with the Jazz governor set to about 72 %. An 11T might work better; although the power at this headspeed is VERY impressive. It probably rivals my heavy 5 cell setup; but the 5 cell 2000 mah setup has a lot more flight duration.
I strapped the 100 gram WattsUp meter to the skids to check the hovering and climbout current. Hovering is about 14 amps and hard climbouts at 10 degrees of pitch peaked around 24 and a half amps. (again, these current readings were with the extra 100 grams of weight.)
It's pretty frisky; not as frisky as the 4 cell t-rex but definitely more frisky than most 3 cell setups I've seen. The lighter weight definitely helps. The most amazing part was the motor temperature. It was only warm, very slightly warm. Just a little above ambient temperature. My Mega motors would have removed a layer of skin by comparison.
I haven't checked the flight times but I don't think it's going to set any records. During hard collective maneuvers the voltage will sag and if these maneuvers are done near the midpoint or end of a flight the Jazz lipo mode will likely sense the lipo minimum voltage during the sag and initiate the slow shutdown a little earlier. There were already some 9.8 volt sags during the first two minutes of the flight so it would probably be wise to do the 'fancy stuff' at the beginning of the flight.
I do like this setup but after having played with the 4 and 5 cell setups I'll likely switch it to a higher voltage eventually. The lower current levels in the high voltage setups just seem less hostile to the batteries. My little 3 cell 2000 pro lite battery (which is normally part of a 5 cell system) was warmer than it normally gets in the 5 cell setup. In fact it may have suffered some ill effects. It looks fine, and it takes a charge just fine but now the middle cell seems to trigger the balancer more than it ever has in the past. the new higher C 2100 pro lites would probably work better than the ones I'm using. YMMV
Oh, when I first fired up this t-rex it had the shorter 315 mm blades on it because it was all I had. The next day I installed the 335 woodies and it made a VERY noticeable improvement in friskiness.