Honestly I don't think that being a great developer is quantifiable in the sense that you can feed some metrics into an equation and come up with a number. If you do that, even poor developers are smart enough to work the system.
Here are some signs of a good developer, IMO:
* Writes code that can be easily understood, even when the task at hand is relatively complex.
* Removes code on a regular basis. (Net LOC added might even be negative)
* Asks good questions to clarify requirements.
* Produces good tests, uses them to validate the code they've written.
* Makes proper use of libraries instead of "re-inventing the wheel".
* Makes good review comments on other developer's code that make it cleaner, more testable etc.
* Documents complex systems so that the next poor sap who owns it won't be completely lost.
Obviously if you're measuring by LOC added, stop it. That's in direct opposition to most of these principles.