Latest steam version runs very poorly for me while an old pirated version runs very smooth, can I use it for speedrunning (in solo of course)?

I say go for it. As of now, we don't know much about the differences between each version. Fastynator was analyzing some differences in the timer between PS3, X360 and PC. All I ask is that if you can, name the version you use when submitting a run. It might help for future strats or timesaves.

ok, thank you! shame that this game isn't that popular for speedrunning, I personally love it

well I just tried doing a practice run and I can already say that nemesis on chapter 4 seems a lot harder that on the latest version, like it has a lot more hp (or probably its just weapon damage which might be lower), also every single grabbing sequence where you need to smah your C key is like 2 times longer and harder than on the latest version, dog sequence for example is nearly impossible without being bitten by it (unless you break your finger) also "spacebar with samurai edge" tactic is broken af here lmao just look at that clip: https://imgur.com/a/dHUMP0S (update: it happens extremely often and not only with spacebar/samurai edge even when enemies are not that close, its almost impossible to run on this version)