Hi TimothyO -
Yup. I've done the same experiment twice now, one with a matched set of PDs about a year ago, then again about 2 months ago with two P1s. I have come to the very same conclusion. It's not even close, Gut/Poly wins the spin contest by a wide margin.
(9x) Donnay Pro One 97 | RPNY Leather | 12.6oz, -12Points, ~335sw | Gut/Ashaway Monogut Red, 60/58 | USTA 4.5 (Benchmarked)