An update for anyone who is interested or may learn something from my shenanigans
As well as buying the Hadron Pegasus I went a bit further overboard, with a Sniper Mechanics GBB cylinder head and a WASP piston, and if the TAC-41 P still disappoints me (as a DMR player) after this I'll call it quits on sniping.
So with all of this installed, using a Rapax 2+ RMS spring and the heaviest piston weight, it's off to my brothers farm for testing it at range (comparing it to my DMR). With the hop set reasonably well I'm finally getting the range I'd expect to, around 70+ meters, compared to around 55/60+ for my DMR, but when I get home this turns out to be at around 2.4 J on 0.48g BB's
Now I'm getting a very good air seal (along with a little PTFE tape on the cylinder heads thread), and using the heaviest piston weight, but it's too hot. So with further testing I'm now on the lightest plastic weight and getting around 2.25 J which I'm going to stick with.
With the Imgur ban in the UK, f**king idiot Government, I won't share any images but for reference hear are the piston weights...
# Stock AEG Piston: 51g
# Heaviest WASP Piston: 120g
# Lightest WASP Piston: 6g
Now I need to pop back to the farm for some more testing at range...