Better piston seal will always help, Pete.
Lighter piston in a wider bore gun will certainly give quicker piston acceleration, Pete, but might not make it nicer / any more accurate as, depending on other set-up parameters, you're more than likely to get greater piston bounce, which is much more detrimental to better accuracy / improved hold sensitivity.
I've sometimes wondered in this scenario, however, if we went for an aluminium piston to reduce overall weight, but a nice, heavy steel top hat (idea here thinking of increasing the cross sectional density) if this may help?
Any thoughts, JB?
Of course, going back to the original flavour of the thread, at our power level, narrow bore is always going to be best.