You might get some pushback from other folks here, but I fly with an oversized pelican case in UC several times a year and have never had an issue. No 'drop you bag into the bin' measuring devices ever experienced. Certainly have never had an issue at the UC Wing.
I don't fly LHR to NY (which would dictate more cabin baggage I suspect) but generally oodles of room in overhead bins LHR to LAX and SFO.
Hope that helps.