I've been using some incannel and offset patternmaker's paring gouges lately for convex curves on saw handles. From my use, the additional length gives you a better degree of finesse, same as with a paring chisel. But the offset (dogleg, crank neck) handle does a couple of things IMHO. First of all, I'm usually using a paring chisel or gouge bevel-side down. With a regular paring chisel, slicing bevel side down, the handle is hiked up in the air, which can sometimes make for an uncomfortable angle and less control. With a crank-necked paring chisel, the paring action takes place in-line with the bevel. Kinda easier to show than to write about it.
For sliding dovetails, there are a couple of special purpose planes, the Stanley 444 at a mere $1000, or there's an Ulmia type out there. I think Lee Valley sells it. You could also use a special-purpose stair saw with a batten as a combination fence and depth guide to create the angled sides.