This was my plan two years ago. I had an external gate on my setup. You are doing exactly as i had planned. I got so far, that i sprayed a 55 shot with my t28 setup @ 20PSI, on race gas. Produced so much power that my sprung 6-puck clutch slipped like the dickens! Dyno graph just disappeared. Anyways, i made 328whp off the spray, and never got a decent dyno run down on the spray.
Basically, race gas + T28 + external gate + 75 shot + supporting mods should net you near 400whp.
Just be really careful, because you WILL be pushing the limits.
Get an external gate to prevent boost creep while spraying.