Interestingly, a 68060 seems to have similar troubles with MIDI music as my 50 MHz 030 Blizzard, so perhaps it's not (only) a question of lack of raw CPU power.
It's a known fact that other than emulating a barely expanded A500 WinUAE is biased towards user-transparent optimized performance than making an actual replica of the equivalent real Amiga setup. If you "snoopdos" ScummVM AGA under WinUAE you'll spot some "uae audio device" working together with the expected paula AHI stuff, which could be adding some "magic" of its own in order to get MIDI music fast and smooth (which seems to be so difficult to achieve in our real Amigas). Of course that's just a wild guess of mine ^_^'
I've just tried Leisure Suit Larry 1 with 1.4.0. First attempt: failed... eer, I mean, I couldnīt play the game 'cause I failed the maturity test questions... So now I know I know less about grown up life than my late eighties self!!!
(keyboard shortcut to skip the questions didn't work, btw)
OK, so on further attempts I get there and... It works with music in default position, but rather choppy and keyboard is unresponsive, making typing commands a real pain. With "no music" it's a bit slow, but nicely playable!