I find myself questioning the performance gain of minified JS files.

I screwed up recently in rolling back changes to a JS file at source control in that I did not give its uglier sister the same attention and I created a bug. Do we need this overhead? How much of a boost is the minification really buying us? I can't believe that it makes anything twice as fast. All that can come out is whitespace and what you might think of as "privately scoped" variable names in a C# parallel, right? (The later get renamed to something more terse, like "x" or so.) Is that going to decrease load times a by a mere 25%? Is there some way to check?