I'm on standard cams and don't really see any great reason to change.

Are you suggesting that the boost level affects the valvetrain with respect to interference or am I misunderstanding you? FWIW hitting the limiter at 6800 we were getting 370bhp at just 16.5psi.

I note that burton and ggr are both doing "'soft duplex spring" kits for around a tenner a spring. If that's all that's needed to raise the limit then it seems like a no brainer to do it next time I have the heads off any of my engines.