I've tried UC hybrided with Kirschbaum syn gut crosses in a '21 VCore Pro 97 and the combo was awesome. The syn gut crosses gave the UC mains some nice added pop, and while I suspected the UC mains sharp corners would shave down the syn gut crosses into oblivion in no time, they actually held up quite well over 8-10 hours, with snapback being pretty well retained during that time. It seemed as though the flat sides of UC were making the bulk of the contact, less so the sharp corners, and overall, I was pretty pleased with the way the string bed aged, all things considered. As a side note, Kirschbaum syn gut probably has to be the best deal in a tennis string, period, at <$40 per reel (on Amazon at least).
Another sharp square string you might want to look at is Grapplesnake Game Changer. GC is even ever-so-slightly more sharp than Ultra Cable, and holds its tension better over time. It's also slightly softer in feel, especially the green color (silver plays slightly more crisp than the green, but still a tad bit softer than Ultra Cable).