nitrous loves high compression, high boost loves lower compression. Your SAFEST bet on a turbo car with nitrous is to use it as an intercooler sprayer. Think of it like this, for every 10 degrees you cool the air coming into the motor, you gain 1% more power. SO, since nitrous is about -340degrees comin outta the bottle and hitting your intercooler, you'll get some nice gains. You never wanna spray nitrous below 2500rpms into the motor. So unless you are using a T78 or 88 where n2o can be injected into the turbo itself to help spool that monster, you won't need it.
What rpms do you launch at??? If you are holding the revs at 3K before you run, don't you think you are producing some exhaust?? Don't you think you are SPOOLING your turbo? Please god don't use the spray to spool up to 3K on a smaller turbo, you'll be a statistic very shortly.
Tuning a motor for nitrous is much more of a pain in the ass than most people think. In order to properly tune a motor for n2o, the bottle must be at the exact same pressure for EVERY dyno run. That is a pain in the arse fellas.
The biggest concern with nitrous is having a cold enough plug, good enough spark and plenty of fuel. If you lean out the motor when you spray, then the chances of doin that again with that motor will be slim. I've seen wet kits being used and the fuel nozzle clog on the kit when the guy sprayed. It's ugly.
Do it smart and you'll be safe.