If the "Sport" comes with 16" wheels and a 5-speed transmission, it sounds like Mazda changed the package names for the NC in '07 (they did the same thing with the RX-8 ). In this case, it sounds like your "Sport" is actually the same as an '06 Base.
A quick look on Mazda's website shows that a Sport is missing the following equipment compared to a GT:
- 6-speed (only available with a 5-speed)
- Fog lights (standard on GT, only available w/ Convenience Package on Sport)
- Cruise control (standard on GT, only available w/ Convenience Package on Sport)
- Power door locks (standard on GT, only available w/ Convenience Package on Sport)
- Remote keyless entry (standard on GT, only available w/ Convenience Package on Sport)
- Steering wheel with speed and audio controls (standard on GT, only available w/ Convenience Package on Sport)
- In dash 6-disc changer (standard on GT, not available at all on Sport)
- Bose 7-speaker stereo (standard on GT, not available on Sport)
- Heated leather seats (standard on GT, not available on Sport)
- Suspension Package, including Bilstein shocks and limited slip diff (optional on GT, not available at all on so-called Sport)
Sounds to me like there's a whole lot of differences between the two models that you've missed.
Here's an example of Mazda package renaming confusion: an '07 "Sport" RX-8 is actually identical to an '06 "Base" model 6-speed RX-8. By contrast, an '06 "Sport" RX-8 comes with HIDs, traction control, and fog lights, which are all noticeably absent from an '07 "Sport", even though the packages share the same name.
Honestly Billy, maybe you ought to spend five minutes on Mazda's website familiarizing yourself with the different packages before you spend $20,000 on a new car. It might save you some heartache down the line.