I have both. I have a slight preference for the 0801 because it's a flipper design and I have personal issues of long standing with thumbstuds. That said, the 0550 is a fine knife. OK, awesome--happy?
Neither is a slicer of any sort. Don't let anyone kid you. I pried open a watermelon with my 0550; I can't say it cut it open except on that initial cut. The blades are chubby and chock full of stiffness and strength. Sometimes there's a need for that. However, if you're looking for a slicer, you should shop elsewhere. Seriously. I had to go Spyderco for that very reason. The horror.
The 0801's metal scales don't seem to bother me, but I'm not out in the cold and wet trying to do rocket surgery on a downed fence with nothing but my pocket knife and a spare pair of socks. Other people may have different experiences which seem more valid given your daily environment. Me? I'm more or less an office worker with a hobby farm. I have whacked down saplings with my ZT, but really, that was nuts and I should have gone back to the truck for a saw. YMMV.
To me, the 0550 feels larger in the hand. I wear a medium glove and again, I'm not a lineman out in subzero weather trying to open my knife, nor do I anticipate being stranded outside my hotel and have to survive for a week with just a knife and pocket lint. You guys with the bigger hands, the 0550 may well be the way you want to go, assuming you don't prefer the flipper of the 0801.
Again, not being a true hard use guy, the ergonomics seem decent in either case. I'll also posit that your experience of the ergonomics may be driven by both what you use the knife for, and your own hand geometry (that said, there are some terrible knives out there and these two are not among them, IMO). I have a poorly healed boxer's fracture on my right hand that impacts how a knife feels to me, for example; my experience may not be your experience. Still, they both feel quite good in my hand, for what that's worth.
