id get the base without sportpackage if i knew i was going to mod it with my own bits.
the Z's sportpackage is just a conveninece package for people like me who want the bits without the hassle of modding. i do a lot of DIY on my cars, but on the Z i thought the stock setup with sport package was good enough for street.
the package is actually pretty damn good imho...especially if you bought the car at invoice like me.