Time to go 6 gives the impression that Cheyenne has a large capacity and could potentially be very good in a holding contest. It would make sense then to put her up against (from the list of available models) Rachael, Carissa or Beverly. Beverly hasn't done a holding content and I imagine she'd be very competitive, so she would my vote.
I don't know if it will be close at all if it's Cheyenne and Constance, with Constance having such a slender frame and probably nowhere near the same capacity. These contests have had some big surprises though.