I use the Flyer (B17 with rear springs) at 210 pounds and like it very much. I suspect that more than 250 pounds or so might compress the springs too much, but couldn't say for sure.
I really like the look of the front loop saddles (the twisted springs on the B33 are fantastic, IMO) but my trouble with multi-rail saddles is that they all require two-piece seatposts which offer limited adjustability of the seat angle. I find that the angle of a Brooks saddle is absolutely critical for comfort, so I really need a two-bolt micro-adjust post with them.