I don't know if this makes sense to anyone, but I like (and usually expect) to see about 10% rise in my BR monthly, which may be overly optimistic (is it?) but that's what I've been seeing the last year or so. Last 2 months saw a 5% loss respectively, but that's the variance at play (or my sloppy play -- I do get sloppy sometimes, gotta stop that).
So you can figure from there. To make a living at that rate, you need a pretty hefty roll.
Also, online, the expectation changes as you move to high limits. I don't know what happens up there much.
But by way of bragging, I saw a person sitting alone at a bunch of 5/10 to 20/40 limit stud tables recently. I jumped in at each level for a few minutes, took down a few pots, and left (hit and run). Kept it up till I had a few hundred bucks, then he stopped anteing with me... he he he