Aside from the PAL version presumably running at 50fps instead of 60, are there any notable version differences?

PAL/JAP - 100% EXP, 100% GOLD, 100% DEFENSE, 100% HP US - 75% EXP, 33,3% GOLD, 150-200% DEFENSE, 100% HP.

That is a generalization of how it looks. US is hard mode. I did a run with PAL version got 11 hours (no slots). On US you are looking at 10:20 I believe. If you are looking to speedrun PAL version I made a guide for that (it is very up to date with fastest NO SLOTS route). You should be able to get close to US times with it (10:20-10:30 even if PAL is running slower). If running JAP version you are looking at times like 9:30 with a good run. PAL is different because you need less grinding and is much easier.

Holy crap I've been playing the US version. No wonder I was getting wrecked.

I made a hack that changes the EXP/GOLD to match PAL/JAP, if rules changed maybe that could be allowed in runs.

I was unaware of differences in defense between versions, can someone give an example? I might be able to change that too.