I have just had the pleasure of a trip back to the UK from PER to attend a wedding and see family and friends.
On the DOH-EDI I was on the 787 in Y, its a total disaster for me, I'm 6ft4" and luckily not that wide. I sat in the seat and my knees were only about 1-2cm from the hinges of the arms of the seat in front. The seats are also not that wide and make you feel more cramped, we both noticed a huge difference from the 777 from PER-DOH.
Even though the routing is great I will be avoiding it in the future if I'm going to be in Y, I would much rather route through LHR or somewhere else in Europe before doing that flight again!