It depends, your mileage will vary.
A few things to consider:
- Have your profiled your code to make sure it's running optimally in MATLAB ( |>> doc profile | )?
- Have you listened to Code Analyzer messages regarding performance?
- What is your code doing? For some things e.g. fixed point or signal processing the C will likely be faster. For linear algebra, ffts, etc., I doubt you'll out-perform the libraries MATLAB uses.
