My friends non-i/c'd turbo junk has a speedo that moves faster than that, gets better mpg, AND its more reliable. Just saying...
Gen V's are overrated, i've been there on the smallest of small pulleys, it wasn't the slowest thing in the world (trapped 110mph on a crappy tune) but for what i could do with a turbo kit vs a supercharger the money is better spent on a snail. Do it, local selling everything your gf needs to fully and officially smoke the shit out of your Z.
I hope i'm the devil on your shoulder pushing you to push your gf into a decision that YOU'LL never regret, but her..
it's not important. She can spend all that money, then when she hates the car you can be the awesome bf and offer to buy the car from her.