Apparently, some people like to put poly strings in the mains. Personally, I'm not sure why. The way that I have always used hybrids is as follows...
Gut mains - this is where you get your feel. When they're fresh and resilient, you will get plenty of spin from them. In fact, you get that "indescribable", soft gut gripping effect that gut is known for.
Poly crosses - several pounds looser in tension. Why? Because poly is so stiff that you want the softer gut mains and the stiffer poly crosses to "even out" in terms of tension. The poly will then dampen the lively gut string to give you great control, and yes, great spin. The poly is also known for preventing the gut from "moving around" out of place.
Overall, this produces a soft "gut like" string job with good control and spin. No, it will not last as long as poly mains (or an all poly string job), but no string job is meant to last forever. This string setup will be very playable, and it will have pretty good durability. I think this setup plays more resilient than any other string job I have ever used.
If you want to put the poly in the mains, then, by all means, knock yourself out.
~GG