To the surprise of no one, going for the thinner and lighter GS66 with GeForce RTX 3070 graphics will mean accepting a cut in performance when compared to the thicker GP66 equipped with the same GPU.
https://www.notebookcheck.net/The-130-W-GeForce-RTX-3070-MSI-GP66-can-be-15-to-30-percent-faster-than-the-95-W-version.533277.0.html