Ok, maybe I'm confused on what the original question was?
I said they were very close to the same performance wise, NOT THAT THEY WERE INTERCHANGEABLE. Sorry if it sounded that way, I also don't want anyone hurt.
Having said that, I have also reloaded for both, and unless you EXCEED recommended max loads, ballistics are very similar for both rounds.
If you load it HOT that's your business, but in the same barrel length, allowing for pressure limitations you won't see a huge difference. 150 to 200 fps is not a huge difference to me, considering the 100 grain psp is a hunting bullet. Now if you're taking shots at deer at 600 yards you may have a slight advantage.
Let me know how that works for ya'. I can't shoot that far, and be consistant.
I don't think the original poster has any intention of pushing the limits of the 6mm on the reloading bench, although I could be wrong? I think he was just asking what a comparable round would be, and I still think the correct, real world answer to that question is the .243 Winchester.
I also don't think he's looking at a rifle with a 24 or 26 inch barrel, that is an assumption on my part, but probably not likely. Look at Tikkabuck's ballistic chart and honestly tell me there is an arguable(real world) difference.
You may be able to hop-up the 6mm to close the gap between it and the 25/06 remington, but I don't think that's what he's asking here.
Sorry if am offending anyone, sometimes I think we take a simple question and make it almost silly by arguing tiny points.