I'll vary greatly dude, like anything in this game. Individuals vary. Hypotehtically though, if everything were ideal and you were able to increase each and every single week for a year (which I don't know of anybody who ever has, or could) and loading 2.5kg each week to Squats and Deads and 2.5kg to Bench and Press fortnightly, you'd end up with +130kg to the lower body lifts in a year and +65kg to the upper body lifts in a year.
Interesting, regarding pulling Sumo, are your legs short in relation to your torso? You're not a short guy right overall? I've got a mate who pulled Sumo exclusively for quite a while, he's a couple inches taller than me (6'3/6'4) but his legs aren't long in proportion to his torso. Seems to be that either shorter guys or guys with a longer torso get the most out of pulling Sumo.