Ive flown both the 777 4cl PEY and 350 PEY and I like the old seat more to be honest. In the first row you also get a leg-rest which you can extend manually (ask FA if you don't figure our how to).

The A350 PEY leg rests are now available at every seat though which is nice if you don't get the first row. Also they can be extended automatically by pushing a button.
I believe that if you're 175cm+ in height it does'nt matter anyways since you wont be able to really use the leg rest anyways.

As for the seat comfort I found the old 777 seats to be better.

If you fancy a better IFE then go for the new 350 ones which also offer the new IFE system and bigger screens. Obviously design etc is 'newer' and 'nicer' on the 350.