I don't think we know yet. In "warmup" / "acclimation" trim the one I regularly see at track days is 2-3s faster than their 765LT. So maybe 1-2 faster than Senna? It was casually running 1:36s at Sonoma with "I don't know we'll see what happens when we start changing / optimizing things" seconds left in it.What are the 720S GT3X lap times, compared to the Senna, with a pro driver?
It's a little hard to compare, the 720GT3X is a highly configurable aero / mechanical platform, the Senna is not. It's a performance matrix of tires, mechanical setup, and aero setup. In the near term the lap times are going to be limited by the owners / drivers just getting up to speed on what a car like that can do / how to configure it. It's an amazing opportunity to learn / get comfortable in a race chassis without racing, an awesome thing from a driver development standpoint, but also a fundamentally different challenge than showing up in a Senna and running it at the limit.
I suspect over the next 12 months we will start to see them converge towards a repeatable limit, but frankly even in a professional team's hands this car would take a few months to master / test / sort. In casual track day settings that extends to a lot more seat time even with professional coaching / engineering. I'm really glad to see it get driven, there's nothing like being passed by one on the entry to T1 / T10 at Sonoma, goosebumps.