Transat's economy seat pitch isn't as bad as it used to be and it can be practically the same as AC or UA's is in the back.
I would compare the Club Transat hard product to UA E+ as it's roomier economy, though they do give you an upgraded set of perks like dedicated check-in, priority boarding, better meal with drinks, greater luggage allowance, etc.
That said IMHO while the upgrade on TS is a good value for what you get I personally would save the $800 and stick with the seat you have in the back.