If you want opinions I will give you mine. I believe anything more than 14" loses accuracy. I would go with no venting and .690 bore. To me it is not worth $45 extra to get a little venting. All you get with that is less noise. Is $45 worth less noise, not to me! If you want to spend that much you may want to look at a J&J edge elite kit or Smart Parts Freak Jr kit.

BTW welcome to the OG. Feel free to ask questions but, make sure you use the search function. Some of what I covered here can be found in other threads. And as per tradition, "Washer first then Oring, tombstone holds them in place."

EDIT: I fixed my post. I put less than 14". I meant more. I with Millslane, I like a 10", 12", or 14".

__________________
If vegetables are bad and some people are bad, then are some people vegetables?