I haven't flown the AC 7M8, but I have flown many many 7-8 hour narrow body flights on TK's 737-900ER's. Lavatory access highly depends on whether you are on a day or night flight and how full the plane is.
That said, I did get on an ET 7M8 recently and found it a lot more comfortable than the old 737's. Perhaps it's just placebo, but I did think the flight was a lot quieter than the old 737. And the old 767 is not exactly quiet either, compared to new generation planes.
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