Well, my first question would be: do you have a 6.5-06 or a 6.5-270?
And the answer to that question may give some guidance as to what brass to use.
Now that you're going "What the Heck is that moron talking about? " I'll explain.
270 brass (and 25-06 brass) is a hair longer than 30-06 brass.
So... you might avoid a bit of trimming if you use 30-06 brass to make 6.5-06 brass.
Now, to complicate things...... I suspect the wildcat commonly known as the 6.5-06 is actually the 6.5-270. Or, in other words, the chamber was cut for the slightly longer 270 brass to start with.
Might be a good idea to find out before you make your brass.