The only "50" I used on my two H3v's was the 55f1.8 in both the Super-Tak and Super-Multi-Coated Tak versions. Almost bought the SMC Tak 55f1.8, but, decided against it, since the early Super-Tak lens was fine on my last H3v. I did consider getting a 50f1.4, but, since my second H3v came when I'd been mainly shooting Nikon, I figured it wasn't really worth it. If I come across a black SV and have enough cash to get it, I might pick up one with a -4 diopter, and equip it with a 50f1.4, 85f1.8, and one of the 35mm Tak's. Just to be able to relive my non-metered Pentax days, with a better fleshed-out kit.
Oh, and, yes, the 55f1.8 is a real nice lens. I would say that it's just as nice as the Nikkor-H 50f2, which means it's very contrasty and sharp with good bokeh.
-J