I prefer poly mains and multi cross. String the multi 4 lbs tighter. Only time poly should go in crosses is if gut is in the mains.
With multi in the mains and poly in the crosses, the poly isn't really adding anything to the party. It's not providing much more spin than stringing a full bed of multi. I would guess that the multi would snap pretty quickly too, but I've never performed long term tests of that setup.
With poly in the mains, you're adding extra spin potential and taming the power of the multi. With multi in the crosses, you are increasing the softness, power and feel of the string bed.