What psi u running with Revo?

I went to my favoriate local shop, TKOMotorwerks in WA (free plug) today to have a revo tune-up today after upgrading my non-piston Forge DV (for sale so make me an offer, I will ship) to a Forge007 over the weekend myself. I was previous running 15psi and am now running 18psi. I have exhaust, downpipe and (as of tonight) modified my stock air box (using a DIY found on here). Just wondering what psi you guys are running "safely." My tuner says we could go 21psi but honestly, I'm in no rush because this is not my project car but rather gentle sleeper. What are you guys running with your Revo? I bought some injectors but may sell them because after this car is paid for, I'm going straight for an RS4 (4 years from now). So...