I fly this route often, have you thought of paying for extra legroom seats if you do not want to go full premium economy, it is much cheaper? Great to hear premium is back up to 35", last time I flew I vowed never to travel with TCX again as I found the 34" pitch still too tight and uncomfortable, the armrests are fixed down and as a six footer I would rather pay BA the extra for WTP. If you look at the CA website though it says TCX is 34" and Air Transat is 35" so may be worth checking. IFE is poor but the crews are always friendly and service adequate considering what you pay. Only once would I describe it as really good.
I have never flown down the back end but have relatives who are regular flyers who say it is pretty uncomfortable and very cramped, if you are on the tall side seriously think about upgrading. It is also great not having to stand in a long line to check in plus the extra baggage allowance.
On the plus side I have probably made a dozen crossing with TCX and they have always been on time and no problems with either the CA booking process or at either end.
Hope that helps.