Well, it really depends. I don't know how well you can drive, but it seems fairly well. If I knew what you dyno'd right now with your current mods, I could give you an idea how much more the big turbo would knock off. Do I think you could knock off a second, possibly, but it would be pushing it. There would be alot of other mods needed, in terms of suspension and traction that would need to be addressed first.
If you were running slicks, then heck yes it would, as slicks would likely knock .5 off your time already (if properly used). Traction will be the biggest factor when you start adding tons of power.
On our latest big turbo/auto combo we made 350whp. Thats quite stout. I am not sure how it equates to your current numbers though.