I think about the HW50 and HW35 as being in the mid-power class (max 12-ish ft lbs), and the HW95 stepping up into the magnum power segment (at least for quality, non-bucket-of-bolts springers).
So, for me personally, if I want something higher powered than the HW30 (which I love shooting), then I go for the HW35 (or FWB124). An HW50 can make just as much power as the 35 and weighs a hell of a lot less, but I love the big, heavy, old-school qualify feel of the HW35. It just feels right to me. That said, practicality is not my primary driver here.
I have a 70's vintage HW35 in .177 that makes only about 9 ft lbs....but man does it shoot nicely. Shot cycle is sooo nice. Currently scoped and great on the bench. I also have a modern .22 that has open sights on it and is a fun plinker with a nice .22 pellet twack and lots of guessed holdover shots. Lots of fun as long as I'm not walking too far. Although what it really needs is a nice leather sling...I'll have to add that to the shopping list.
When I want more power, I step up to the HW95. A great all-around gun. I love the R1/HW80 on principal and have 3 of them, but almost never shoot them. The 95 makes almost as much power in a lighter, more compact package.
OP - if you already have a 95 and a 30, then I think of a HW50 as a boring middle child, whereas a 35 would be something quite different (bigger than the 95 but power that is about mid-way between the other two). That said, as much as I like my 35's, if I had a 30 and a 95 and wanted something in the middle power-wise, it would be a FWB 124. In fact, the last three rifles I would ever part with would be my peep-sighted HW30, scoped HW95, and open-sighted FWB 124. But I'm a long way from that today and have zero plans to downsize to that!