There are improvements in many places already, and many other known improvements will be implemented. But, yes, the biggest time saver so far is the version change, I won't deny it.
But without some other major game breaking glitch, it will be pretty hard to improve the published run using the USA 1.1 Rom.
I've tried and at the end of every stage I saw it falling behind and behind. Not a pretty encouraging sight, I tell you.
edit:
here's the WIP I promised;
http://tasvideos.org/userfiles/info/17058681638860183
Improvements so far;
Mainbrace Mayhem new strategy.
A really small improvement on Lava Lagoon.
The strategy from the 102% run was implemented on Kleever.
edit2;
The set up of the high jump was improved a little in Slime Climb.
One of the barrels of Bramble Blast was skipped.
edit3;
For some reason the game is now running just great on BizHawk 1.8, so I'm updating to this version.
Also, by pausing the game you'll have the same "fanfare problem"; it seems to speed up the music.
Now I'm not so sure if I want to submit this run, but I'll finish it regardless. Maybe we can get something good out of it.
edit4;
I'm at Hornet Hole, 5485 frames ahead. I'm sorry to keep comparing this to the published run, but it's the fastest so far.
edit5;
I forgot to post the new WIP on my previous edit;
http://tasvideos.org/userfiles/info/17136561383857693
edit6;
The differences in speed and physics on Hornet Hole are driving me crazy, two days and I barely made it to the checkpoint...
edit7;
I'm still at Hornet Hole, but at least I'm making progress. As a side note, the tricks and movements used on this stage will be slower in comparison with US 1.1 Rom.
edit8;
Whew, I'm finally out of Hornet Hole!
edit9;
Bramble Scramble completed,
02:47.97 ahead now.
edit10;
another interesting difference between versions; Dixie plays the demo mode instead of Diddy in some of the stages.
edit11;
I'm fighting King Zing,
03:09.33 ahead now. New WIP coming soon.
edit12;
New WIP;
http://tasvideos.org/userfiles/info/17265389619791919