I'm going to migrate to 4.1.0 before the official cutoff.
And as for having two gateways?
I'll keep the second one alongside it.
As for being able to cleanly separate the two, well, let's be honest, I can't really say wich user came from where either.
Which is all to say that, even with my decision to migrate, I don't feel bad about having a second gateway, just in case PayPal is just not living up to all its promise and I need it.