Trim to shortest or size to stretch. I only need to do straight walled once to have consistent crimps for the life of the brass. This is mostly range P/U or used, but new also every once in a while. I use an inexpensive caliper as a go no-go gauge. I can tolerate a bit of variation in the roll crimp without it making a difference, I'm not so accurate a shot that it will matter. I just don't like crimps that are above the groove, below the groove, and in the groove. Top, bottom, or middle of groove itself is fine with me.
I guess a few powders that are more dependent on pressure for good burn it might make more of a difference.