ALU Power Rough and 4G have made the biggest impression on me when it comes to poly strings used as a cross with gut. Among all the different polys I've tried none allowed me to really lay into the ball and swing fast while keeping the ball in like 4G. I can produce an amazing amount of top spin with 4G. What may be happening is the ball is flattened more with 4G kind of like when you hit with old tennis balls. A fast bat swing combined with mass reaps the benefits from 4G.
Wilson BLX 90 - Wilson Pro Overgrip - 13 ounces
Wilson Gut 16 / Luxilon ALU Power Rough 16L 50/48 pounds