For me, the GPT is almost a different shoe in terms of what the ZZ was. It's about 18% heavier, slightly less spacious in the toes, a smidge narrower in the forefoot, but wider in the outsole for stability (which was one of my gripes about the ZZ). I played 2 hours of dubs on Plexicushion and the GPT wear should be around the ZZ, may even slightly better. The court responsiveness is better than the ZZ, which I felt was muddled. It's definitely more stable. The traction was a little difficult to judge on the lateral runs. For net advancement and back tracking, it felt decent and a bit more slide friendly, a little too much for me as I slid too much and touched the net trying to run down a drop volley.
For fit, it's only the toe box that is less spacious. The ZZ did squeeze the tuberosity of my metatarsal a little when I cinched it tight to prevent lace slippage. I don't have that problem with the GPT, and the lacing system I can't say much about as I switched it out for lock laces, because I hated the ZZ hoop slippage.