10% of initial body weight, and keeping it off for at least a year.
That means that, from my highest of 283, I need only lose 28.3 pounds and keep it off for a year, to be considered successful. 283 - 28 = 255, and that's just a shade under what I weigh right now. I'm already almost a "success" by that statistic.
50% of my excess? Well, I'm not sure how much of me is "excess," but say my goal is 160. The high of 283 - 160 = 123 of excess, so losing 61.5 would be considered successful. 283 - 61 = 221. I don't consider that too satisfying either.
A bit disheartened.

So let's recalculate from my present weight, where I've been stuck a couple of months now.
10% of my present 260 would pull 26 pounds off of me, leaving me at 234. Stay there for a year, and I'm a "success." Assuming 100 pounds of excess, losing 50 pounds by WLS would make me "successful" at 210.
It's going to be hard to consider myself a "success" if I'm still over 200. Let's raise my goal a bit, since I was considering 180 as a goal instead. The measure of success by diet and exercise wouldn't change, but let's look at the best calculations for WLS. Say my goal is 180 and we start from my present 260. This makes 260 - 180 = 80 pounds of excess, so losing 40 would make me "successful." Now I'll end up one of the success stories at 220, which is the same as starting me from my high and making my goal 160. No statistical difference at all.
This is a lot to think about.