I think the break point for the extra heavy duty suspension is 245. So if the seat was built for a 220 pound rider, it might be strained for a 285 pound rider. Once the seat has the extra heavy duty suspension, I'm not sure what more they would do aside from larger wings to accommodate the larger butt.
FWIW, I used to get the Russells. They're really great seats, and they really make the bike more comfortable for a bigger person.
I still have a heavy duty Russell for my Rocket III Touring, but I've taken it off. It was built when I was much larger, and so the suspension was the heavy duty type.
I noticed that I was having some grip issues with the R3T, and I was getting ready to trade it. My hands just didn't seem to fall onto the grips like they used to, and the angle was exacerbating some other hand problems I was having.
I took the Russell seat off as I was getting ready to trade the bike and remounted the stock seat. The hand problems went away.
The heavy duty suspension, being sat on by a much lighter person, tipped me forward, and changed the angle between my hands and the trips. This surprised me, but it was a real effect.
When you have Russell build you a seat, they take quite a few measurements, and they want a couple of photos. I've had a lot of Russell seats, all custom built for me, and every one of them has been excellent. In this most recent case, the seat was excellent when I was at the weight I was when I had it built. It was not so great after I'd gotten back to a more normal size.
So ... I think that to get the best performance from a Russell, it's probably worthwhile to have them build it specifically for you, unless your build is very close to that of the person for whom the seat was originally built.