I had (still have, actually) a Quadra 840AV which was the fastest 68k Mac they ever made and it never felt this fast. If they emulated the actual performance of a 68k (and associated hardware) you wouldn't long for the performance it offered. But sure, running a much simpler (and more efficient out of necessity) OS on modern hardware, even emulated, screams on today's hardware. On the other hand, it didn't pack anywhere near the amount of functionality so the majority of the ROM and OS will fit in the L3 cache of today's processors so of course it's fast.