Which one of these three loops is the most efficient? How can I prove the answer?

I've listed the source code below. The three loops are:

1. Foreach over an int array
2. Simple for over an int array
3. For over an int array, hoisting out the length value

...

The third option is to be avoided. The JIT looks for the pattern in version #2, and knows how to optimize it. If you pull the value out into a temporary, it may not optimize it. Of course, you know that because you've been measuring your important scenarios...

via [Eric Gunnerson's C# Compendium]

Hoisting the Length value is ill-advised? Surprising; I'll have to change my habits.