Will this wing stay stable at highway speeds?

Yes. The Si-spec profile is engineered for the factory mounting points and handles normal driving loads. Ensure all fasteners are torqued to your vehicle's service manual specs and re-check after 100 miles of driving.

Does the wing interfere with the trunk lid?

The Si proportions are designed to clear the factory trunk opening. If you've modified your trunk lid or added other rear components, verify clearance before final installation.

What's the best prep before paint?

Sand the surface with standard automotive prep grit, then apply your chosen finish. FRP bonds well to both single-stage and clear-coat systems — follow your paint manufacturer's adhesion guidelines.