So. I've been playing with my N9@1.375 GHz. SR OFF, voltage 1387500.

Wasn't entirely stable. Everything except apps that use GPS worked. Dunno why, but Maps for example crash after a few seconds. After 20 minutes of playing games, watching videos on youtube with firefox and launching apps just for the fun of it, I managed to crash the built-in web browser at sunspider test.

Tried 1.4 GHz anyway and app-launcher just went dark and I had to reboot it.

The speed boost from +375 MHz was noticeable in every part of the system. I would very much like it to be permanent :-) The phone started to get warmer but I had N900 OC'ed to 1150 MHz for months and N9 at 1375 MHz is still cold compared to that :-D