Even with the reliefs, you're going to bend stuff if the belt breaks.
But yeah, with valve timing spot on, no need for them. I've also heard of several people doing it. And Kenny (IIRC?) had smaller exhaust sized reliefs on the intake side, so the valve would have hit anyhow, but they never did.
As to the other question - what is a safe CR? That's a very, very loaded question.
- What kind of fuel will you be using
- What kind of turbo, and how much boost are you planning on
- What sort of HP goals
- What sort of EMS, and how good are you at tuning
- What counts as 'safe' - cramming boost in an engine has risks