Since I don't know how big your map is, how many stamps there are, how many different stamps there are, and how many animated stamps there are, I honnestly can't tell you. I would asume that all of the above are correct, considering what I've seen of your games, which would slow a game down a lot in classic. Once the update is released, it should fix that problem.
Another thing, when you say slow, I'm assuming that by slow you meen crawling, like, say it takes about a minute to move 100 tiles and/or there is a control delay of, like two seconds.
That is all I can say. And really, there isn't a good fix for it while still keeping the same graphical quality. And the entire problem is made even worse by the classic emulation.
--You might try increasing the memory-- (just a passing thought)
I hope that helps in some way.