Jason,
I also questioned some of the manuevers the other poster suggested to demonstrate having mastered a 'trainer' model. I have spent decades building and flying r/c planes, instructed beginners and basic aerobatics at each club I've joined, and flown most types of planes (trainer, sport, combat, quickie 500/200, pattern, scale and twin), but have no experience with helicopters, jets, QMs or giant scale. I do not claim to be an expert only stating that I have some experience.
Presuming proper set up and balance, and an engine near the top of the recommended power range, I believe almost all of the most common trainer aircraft are capable of inside loops, rolls (barrel and slow), stall turns, spins, Cuban 8s, Immelmans, Split Ess and short approaches. Depending on the particular model and the wing dihedral, snap roll and knife edge may not be possible. If not, then 4-point roll and avalanche will not be possible. Some trainers will not stall, they simply mush into a slow loss of altitude, and can not perform a spin.
In my opinion you are wringing the most out of your PT-40!! Regarding your comments on how you perform some of the manuevers;
Fly inverted? Low inverted? Yes. Need to really work the throttle to keep that nose up
I don't understand working the throttle. I fly inverted at the same 'cruise' setting I use upright, 1/2 to 3/4 throttle. With my Funtana 40 I need no elevator, a little forward stick with my Super Stearman, and a little more forward stick on the H9 Alpha. The Alpha is a little tough for me to keep inverted and I work the heck out of coordinating rudder with the minor ailerons during turns around the field. However, a recent student with lots of simulator and electric (J-3 Cub) flying kept his Alpha inverted during four circuits of the field...on his third flight with the Alpha.
Slow roll? Yes, assuming enough airspeed to begin with.
I fly slow rolls as I would in a full size, non-aerobatic aircraft. Put the plane into a slight climb, then start the roll. Use elevator/rudder/elevator during the roll to minimize the nose drop. The amount of nose up climb required to be able to complete the roll with no loss/gain of altitude depends on the specific trainer/sport model being flown.
Stall turn? Yes, into a 6 or better mph wind. Otherwise, its really more of a fall rather than a turn.
Without seeing you perform this, or understanding more, I can't comment. Please provide the steps you perform to do your stall turn.
Short approch? Yep, especially into a wind.
Using a headwind is cheating!
I learned the mechanics of 'short approaches' before I started flying r/c, while taking flying lessons for my pilot's license. The key is in losing altitude without increasing forward speed. The necessary manuever is called a 'slip.' Bank the plane (let's say left bank) and input opposite rudder to keep a straight line over the ground. With the wing angled you lose altitude, but since the nose isn't lowered you do not gain much speed. Bring the wings level, removing the cross rudder just above the height you would begin to flare for the landing.