Actually, aside from size, what's the difference between H6K and H8K?
Both are Japanese flying boats, used for maritime patrol. H6K was introduced in 1938 and H8K in 1942. H8K was developed from H6K, so it was larger and had a longer range. Visually, H8K is distinguished by having it's wing flush along the top of the fuselage, while H6K's wing was suspended above the fuselage by a series of struts.
I wonder if handling that thing was murder to the pilots.
I don't know specifically about the H8K, but it's not necessarily so. Some large aircraft are hard to fly and some aren't; it isn't a direct function of how big the aircraft is. For instance, the American B-24 Liberator bomber was notorious for the physical exertion required to operate it, but its similar-sized contemporary, the B-17 Flying Fortress, was equally renowned for how easy it was.