Firstly, could you elaborate what code you're looking at? Square have never shared the source code for these titles and were not even practicing real version control at this time (see: Eidos FF7/8 debacle)

Secondly, it absolutely will run slower. Animations will take longer to complete; FMVs will play at a different rate ; controller sampling will be reduced.

My scepticism isn't coming from hearsay or ignorance: I have written PlayStation software, and PSX software is not parallelised, even though it can support threading and cooperative concurrency. The control flow of the title is very locked into the VSync loop, from your first ResetGraph(0) right to your final DrawOTable(*p).

In addition, I have done a bunch of reversing work on the other two PSX games, and they are not monolithic programs. They can't be because there simply isn't enough RAM to store the .TEXT of the entire thing at once. So when you say "the source code", I'm inclined to ask - for which module? The kernel or one of the overlays?

Good for you. When I say the source, I mean all modules, the kernel, the graphics, everything. Cheers. While we didn’t use version control the way we do today, we still had it… some of us also made copies.

It’s not lost except to maybe Square Enix’s corporate but they don’t know where anything is.