My N9 (Singapore version preordered) has been solid at:

1300mHz+1.275v and smart reflex on

Uptime of 5 days with GPS usage, games, you name it. AWESOME! Looking at Battery Graph is seems battery usage has IMPROVED over stock. Admittedly I was worried about usage so i was probably monitoring usage closer than normal. Battery Usage app indicated idle usage of 28mA with no chat active. Active consumption did seem high at over 300mA.

I get an almost instant reboot at 1.25v. I am thinking about trying 1400 mHz now.