They normaly overbook the flights by 10% as many don't show. If it only shows near full you probably won't have a problem, there could however be many more than you on sby tickets, not shown in the figures you are looking at. If there are seats in any cabin they will load all the pax including the staff. They will decide on who to upgrade and it may or may not be the staff. They look at gold card holders etc first, and if it's evident there will be upgrades, they may even start to do this before check in starts based on frequent flyers etc. dress smartly, be polite, and you may well get moved up. Unlikely if you have small children with you though.