Is my motor done?

[SMatyac]

I picked up my s14 the other day and it has an sr20det with a gt2871r .86 ar, and has 880cc injectors, and it ran like a champ.
On the way home i want very hard on it at all, but it started shooting an oily mist out of the BOV, and then it started missfiring when it hit over 15psi. it doesn't smoke unless it misses. Occationally it will hit full boost, i can floor it and it runs awesome.
I took it to a shop, they pulled off the oil filler cap and it had a pretty strong pump of air coming out of the hole.
The shop said it could possibly be the headgasket, but it could also be my bottom end.
My car doesn't have an oil restrictor on the turbo, and it doesnt have a catch can, is it possible the TPS sensor only sometimes works fine, or do you think the pistons are fried?