I am a huge fan of the poly's in the crosses. I don't normally get to use gut, but I use gut-like multis. With the poly's in the crosses you get more power and spectacular directional control(huge angles).
Well I just tried Alu rough in mains and soft multi 2 lbs less in cross on a Ki 5 and it felt sweet, but will try the reverse sometime as you make it sound great.
A year ago, I would have said it was a waste of money to put gut in the crosses with ANY string. However, I have strung it up for a couple of guys that really get some big spin putting ProHurricane in the mains and BDE Perf. in the crosses.