Not sure where NN gets his 56 days from. You'll get 4 x 7 day blocks of leave (which you cannot work in) and 2 x 7 day Duty Free Weeks, which you can choose to work in. That makes 42 days leave/holiday/call it what you will. NN may be including 'Wrap' days which are a couple of days taken either before or after each block of leave/DFW which you cannot be rostered to work on if you choose not to be. However these days are not leave as such as they attract no credit, so if you choose not to work on them you'll have to work extra hard for the rest of the month to make the credit back somewhere else. Wrap days should be considered guaranteed days off rather than paid holiday.
As for 4 weekends per year, that is very possible if you are junior. I know junior skippers on the Airbus who have not been rostered a weekend off outside leave for almost a year. Seniority is everything, and if you're junior then weekend working every weekend every month is a distinct possibility.
The 757/767 seems to be a very popular fleet at the moment. For commands this year it was the second most senior fleet in the company after the 744. Workloads seem to be manageable and even junior pilots seem to get the occasional long haul trip. Seems like a nice place to be.