Don't let LOC be your primary metric. 50 lines seems really small to me. With 50 line files, you will end up having an unfriendly number of class files in the solution. Your productivity will be dampened by all the navigation you will be doing between files and your IDE will always be littered with too many tabs. I personally try to organize classes into logical groups by namespace first. On a class by class basis, I try to make the code smaller and easier to read. Sometimes, class files do get large. I start to get a sick feeling when the class file is 2000+ lines. Anything less than that, I deal with on a case by case basis.
