A subject close to my heart living down here with typically 5-40C winter-summer temp range.
Having chosen the TX platform for both my FT & HFT springer rigs I have spent more than two years experimenting and testing numerous "tunes" / components to measure basically two key criteria:
1. Reduced sight picture movement (i.e. the ability to view the pellet flight and strike point)
2. Manageable consistency (fps) through cold / hot conditions
Any other subjective factors (feel, noise, twang, etc.) have largely been ignored, with the exception of durability (e.g. service, seal replacement, lube intervals).
I have for now settled on Nick G's lightweight, short stroke, o-ring pistons.
With the right lube regime (another journey akin to the quest for the Grail!) they deliver a winter-summer variance of around 10fps (conveniently 1 skinny washer above the top hat, or with weighed pellets no issue!).
In my testing, everything with a standard type piston seal (LGU, HW, AA, V-Mach, Maccari, Vortek, Aus Custom) seems to expand / shrink considerably, necessitating recalibration. As do the Vortek o-ring noses (which seem to have lousy crush calibration in the first place!).
Happy to share as I could have saved a lot of frustration, time (better spent practising) and indeed money if I had found this sooner
and enough math with the scope behavior to keep the brain cells exercised!.