I've run 24 psi on pump gas and the stock 6 bolt bottom end, but I get about 4* of knock when above 22 psi. All supporting mods:
walbro fuel pump
660 injectors
VP FMIC
dsmlink
Hahn Super 16G

I've known a guy to run closer to 29 PSI on a 16G setup with the same supporting mods with C16.

I was running 20 PSI w/ the 14b on the 6 bolt with a walbro, 660s, dsmlink, and the stock SMIC, but I was heat soaking the SMIC. My intake temps were too high and I was getting > 5* of knock and pulling timing. I was a typical summer night in Florida though (hot and sticky).