i'm honestly really happy with my regular egos...have two in rotation(third I havnt touched yet, back up) and they last me about 6 hours with an LR (I'm a heavy vapor)
It's one heck of a step up...my 510 only lasted like 30min-hour for me...had like 6 in rotation.
But on the other hand....xl's are only like 4.00 more and they really arnt That much larger.
I agree that if you're just looking for a battery or 2, the XL's are the way to go. That is, considering you already have the charger and cone. But $60 for the full kit, with 2 cones and 2 atty's plus the charger AND a bottle of juice simply can't be beat.