I don't believe it will allow you to check previous scores and stuff. 3arc sucks at most everything else, so I doubt they'd keep a database for that. Though they at least did allow community playback from previous games, but that still won't tell you your xper score. I think the most I made was like 50k points in a game of hardcore HQ. Not double xper weekend either, but thank god for "lifetime" challenges :D
Don't know, but most the leaderboards are duds... A lot of people hack the system and have insane scores or kill streaks. Sure you can be good, even great at the game... But probability is that you'd not achieve the score that those boards suggest. I mean you'd have to be 100% focussed the whole time and play a lot without switching off the system.