If you've got any sense at all (and don't need the features in 2.5/2.6) then you won't upgrade a v2.01 PSP yet.

The ONLY barrier to downgrading a 2.01 is that currently no-one has been able to run any code on v2.01, because the only known way to do that (via the TIFF exploit) was fixed. That is the ONLY difference between 2.01 and 2.00.

If code can be run on 2.01 (and there are good indications recently that it can) then downgrading it is simple.

For v2.5, it's a very different matter. No code can yet be run on v2.5, so the first barrier is the same. But there's an additional barrier that no-one has any idea of how to perform a downgrade on v2.5, even once they have code running. If you follow the currently-known downgrading methods, then you WILL brick v2.5.

Remember that if a viable downgrader for v2.5 is released, then v2.5 users will be able to use it. v2.01 users will also be able to use it, by upgrading to v2.5 first.

But if a 2.01 downgrader is released - only v2.01 users can use it. v2.5 users will be SOL.

The v2.01 user-base is also not small. Almost every PSP currently being sold is v2.01. v2.5 users chose to put themselves out of the game.