I've only got bantams for now, so I won't be a ton of help. If you're getting them from McMurray, I don't think they vent sex bantams. I would personally stick with straight run either way, as vent sexing seems potentially dangerous to tiny bantam chicks. I have no research to back this up, just what I know about how vent sexing is done, the fact that almost no hatchery actually does it, and experiences I've seen others go through with sexed bantams.
I've also read that you may need to consider ordering more bantams than you would standard size chicks to keep them warm enough during shipping. I believe I even saw one hatchery had a minimum of 20 or 25 bantams.