So it sounds like you're an RV-6 pilot wondering about transitioning to the T-6? Try it, you'll like it!
T6 Harvards feel like an overloaded gravel truck on a soft wet road for handling,
What made them a good trainer is they are like a C150(under powered /overweight). With retractable landing gear, a hydraulic system, and a CS prop.
While I'm not a high time T-6 driver (125 hrs in type), I disagree with these statements. The T-6 has two types of ailerons, "high rate" and "standard"; perhaps the comments above come from experience in a ship with "standard rate" ailerons? The one I fly has the high rate ailerons and is just a nice flying airplane, very responsive to the controls in all axis.
As far as being under powered... it's really not. Standard gross weight on an early AT-6A is 5300 lbs being pulled along by a 600 hp Pratt R-1340; power/weight ratio is 8.8 lbs/hp. My 1800 lb, 180 hp RV-8 is 10 lbs/hp. Or, compare the T-6 to a Cessna 310R or E55 Baron; they both weigh in at around 5400 lbs and have 570 hp... so in comparison, the T-6 has a better power to weight ratio than a 180 hp RV, a C-310 or Baron. It's a draggier airframe for sure what with the fat face radial engine, but I wouldn't call it underpowered.
The flying part is easy, but it's the ground handling that might get you; it has a fairly narrow gear track and a long tail with a good bit more mass than an RV. If the tail starts to come around, you gotta stop it quick with the rudder, right now. No lazy feet! Once you get the hang of the size/mass and how it affects ground handling, it ain't that bad. Most T-6s have tailwheel steering thru the rudder pedals with the stick held back; push the stick forward and the steering pin disengages to become full swivel. Navy SNJ types are full swivel but lockable tailwheels.
Landings... I always wake up and pay attention to those! I've landed in 12G17 kt crosswinds with it; not fun, but doable. Any more than that, then call me chicken! Three point landings? Also doable, but just not really a good time for me, so I wheel it on. Kinda like an RV-8 in that respect...
Bottom line; these things are just a hoot to fly! The sound, the smell, the oil smoke on startup... rumbling along on a nice evening with the canopy cracked open doing a few wingovers. Man. Now I wanna go fly it! It's true that it's a thirsty pig compared to an RV, sucking down 28-30 gph at normal cruise speeds. But, for me, it's not a daily flyer type machine, so the fuel burn only hurts for a little bit.
For a good read on the T-6, check this out this pilot report from Budd Davisson. That dude can write.
http://www.airbum.com/pireps/PirepT-6.html