So after being tipped off a while ago by Osmorosvo that the Amiga version of the game (playable through ScummVM) has a faster swamp coffin speed, I checked to see if anything else is quicker and how much so. Here are my findings:

During the Opening Cutscene (where you see Scabb Island)

Dos version you have to wait 8 seconds to skip this, on Amiga you can skip it instantly

Amiga saves 8 seconds

The Swamp Coffin ride

To row to the Shack on Dos takes 23 seconds, Amiga takes 12 seconds

To row from Shack to the Shore on Dos takes 19 seconds, Amiga takes 11 seconds

But don't forget you must ride the coffin 7 times during a run (3 times to shack, 4 times to shore). So we have to multiply it.

3 x 12 = 36 4 x 11 = 44 Amiga time = 80 seconds (1 min 20 secs)

3 x 23 = 69 4 x 19 = 76 Dos time = 145 seconds (2 mins 25 secs)

Amiga saves 1 minute 5 seconds overall

The Drinking Contest (from when Rum Rogers says "You drink first" to when you have control of Guybrush again)

Dos takes 29 seconds Amiga takes 12 seconds

Both of them drink from their mugs faster, Rum Rogers falls over faster and Guybrush is controllable almost as soon as he stands up.

Amiga saves 17 seconds

The fall into the Tunnels at Dinky (from when Guybrush's Rope breaks to the scene ending)

Dos takes 7 seconds Amiga takes 3 seconds

Guybrush's long fall is cut much shorter

Amiga saves 4 seconds

So in all playing the Amiga version saves you 1 Minute and 34 Seconds

You may be asking "well is anything slower on Amiga?". The only thing I noticed was the Cutscene inside LeChucks Fortress (after leaving Scabb for the first time) took a little bit longer to skip than on Dos, maybe costing 1 to 1.5 seconds.