Well you do realise 600hp is pretty close to 500rwhp yes?
So if you've heard they are "good" for 600hp, and you want as LEAST 450-500rwhp - you'd certainly be pushing things gonig by that.
That said there is no magical "safe" number for power. Depends on the age of the motor, use of the car, previous life (generally unknown), tune etc etc. Basically how long is a piece of string.
End of the day i use a rule like this.
Can you afford to break it and the associated rebuild (AKA: The $10,000 adventure)?
If you answered NO - stick to Garrett -7s or -9s with 300-330rwkw (400-450rwhp)
If you answered YES - go for bigger Garrett -5s or a GT3788 370-400rwkw (500-550rwhp)