You can't use the 950 as comparison because it is a 90 watts GPU. A large portable device, such as a tablet, can use 10 to 12 w top. So NX will probably be way behind X1, unless it has some extra stuff when docked.
The only Tegra X1 device we have is the Shield console, but even it can have a larger TDP going as far as 20 watts when playing. It's a bit more powerful than PS360. So realistically, NX could be between PS360 and X1. Of course, supposing that docked it wouldn't have any extra juice. Anyway, don't count on a miracle because Tegra X1 was designed as a low TDP SoC for tablets, micro-consoles and embedded systems.