Thanks all, for the factors you eloquently put into words :-)

Read, I think you're right that contra dancers are more familiar with it; and that will help too. The proof is in the pudding though; or the dancing as the case may be. I'd say get three friends and see what the two stars feel like; and if dances feel more comfortable moving faster in one than the other. My kinesthetic sense is that the mill grip can be faster, and the feeling of connection allows folks listing to the beat and phrasing to influence those who might be lagging. It may be a regional variation on how connected folks are through their mill-grips though. 

As yet another variant on the dance that doesn't require stars to go as far, I propose the following for feedback:

Tamlin's Cast-off Cross

4x4

A1

Lines of Four go forward and back

Corner Swing, square set

A2

Gents cast off - behind the one they swung, one place counter-clockwise, to stand next to partner

Ladies left hands across star 3/4, take hands in crossed wavy lines of four

B1

Balance the crossed wavy lines

1/2 grand hey for 8, turn to find partner

B2

Partner balance and swing

The tricky bit seems two-fold in A2, where the gents have to take their momentum that would normally bring them into the middle with a left hand ready and curve it out and around with a wide cast; and the ladies have a 3/4 star without a clear bench-mark of who they're landing on (it's not their partner or the one they swung). But possibly those are minor obstacles to a crowd you could through half a grand hey at anyway...

Thanks again for all the feedback and questions! :-)