I disagree mate, say four years time we move into a 60k plus stadium, and we are still in the same boat performance wise.
Every new stadium struggles initially for a few years to get the atmosphere back or to rebuild a lost one, a 60k crowd will bring in a bit more money, but I'd almost guarantee the atmosphere will be worse at 60 than it'd be at 50 say, unless they do something groundbreaking with the pricing to attract local lads who have been priced out.
I think us building off the bat a 60-65k stadium would be another example of us trying to run before we can walk, same as we've seen with trying to rush a dof model, manager changes and 250m spend on the team has been done.
Juve built a 42k with plans sorted prior to building for a 10k expansion. And what it gave them was packed out crowds, a nasty arse atmosphere and made it fast feel like home due to that, now when they expand they will be doing so whilst keeping those things.
For us, a 50k stadium with locked in plans for a future 10k expansion pre designed into the build would leave me happy, so long as that ensures we build to make the place a proper intimidating ground.
We move into a 60k straight off the bat, I'd worry seriously that a lot of games we'd be 75% capacity after that first season. And whilst monetarily that wouldn't matter, it'd kill the positivity about the move and we'd have a west ham thing about we should never have moved going round quick.