I have a Peavey Ultra plus thats 120 watts. My cab is an avatar 2x12 closed back with vintage 30's. So the total rating on the speakers is 120 watts.

This friday I have a gig and I want to be able to crank it to the columes I want, while still micing it up to the PA. If I leave the channels up and turn the master to like 8 or so will it be fine? Or even dimed? I'm afraid of my celestions to just POP and there they blow. I would imagine it would be fine, or would it?
Don't worry, you shouldn't ever need to push a 120watt amp past 5 for audible reasons.

The speakers will be fine. They are made to be pushed hard.
Mesa Single Rectifier
Marshall 1960A vintage
Rg3exfm1 w/ EMG 85/81
Big Baby Taylor Acoustic
Ibanez TS808
Why would you need it that loud!? Unless you want everyone in a five block radius to be deaf afterwards...
because it's an outdoor gig, on a field. PA will be doing alot of work but having the opportunity to get the tone i want is pretty cool considering i wont be drowning everyone out lol. So it's not just audible reasons, when we rehearse without a PA I leave my amp around 2.5 actually..