Yep. 15-inch Surface Book 2 has a GTX 1060 in it. I don't think there is any thermal throttling, if I remember the reviews correctly. However, the GTX 1060 is in the keyboard, so the GTX 1060 can only be used while docked. When undocked (i.e. tablet mode), the GPU inside the tablet (Intel UHD 620) is used instead.
P.S. The 13.5-inch SB2 also has a GPU (GTX 1050), but only if you purchase the 13.5-inch SB2 that has Core i7 processor. Core i5 version does not have GPU (except for the Intel UHD 620 in the tablet, of course.).