6-7 is fine
8-10 is probably ok
10-12 has been done without issues (trever1t)
12+ i would not recommend personally...

 

On cool days mine is doing 9 was thinking if I ever get the IAC working right may try more. Seems to lose a little on hotter days.

 

That's the consensus around here anyways. But Im sure you know how alot of the guys with forged motors around here came to need them? You always want more, and its too tempting to push it just a little bit further!