The 777 does fly faster but its cruising speed is only 10mph faster according to UA's website.
http://www.united.com/web/en-US/cont...t/default.aspx
If you are a non US citizen, I'd say your chances of clearing immigration and customs and making a connection in 1:10 is slim.
When you say actual flight time are you talking about time in the air? Isn't the fight stats time gate to gate?
I had a westbound TATL last week that arrived 40 mins early and a eastbound today that would have been an hour early if LHR didn't make us hold for 30 mins because we were early. I did notice when it went from a 788 to a 763 they added 20 mins to the blocked time.