I dont know if this is enough time differences to separate the JP and US version.
US version dont have transitions from stage to stage (dont know if is faster than JP as its has a transition).
The big time difference is on any% because on US you dont have to wait for all the transitions, just 1 screen, while on the JP version tou have to wait for every single transition till the boss fight.
1 more thing is on the JP version you skip stages till the boss while on the US it skips around 6 floors. I have not tested to be 100% sure, I just notice the difference on casual playthru.
So with all that info it looks to me that there is a difference enough in time on a speedrun to separate the US and JP leaderboards.
I put together this side by side video to test what Edo mentioned. The video shows there's roughly a 2sec time difference for every screen transition. Stretched across the 60 levels, that'd mean the JP version is roughly 2mins slower due to this.
Cheers!
