Ok, so I guess it is "confirmed", the new Asus G750's will have Nvidia Optimus ...
I was installing the new drivers from the JM download area, and installed the Asus GPU Tweak tool 1.0.5, and it came up with a totally new graphic, but worse - it got mixed up waking up on my G750JH and said "Nvidia Optimus Enabled - currently running on Intel GPU"!!
I had to double check and look at the Device Manager, and sure enough there was still just the GTX780m listed.
It displays the status in the bottom left corner of the dialog, and it disappears as quickly as it displays the status, it took a couple of runs before I could catch the text status, but here it is:
Because it thinks I am running on the Intel GPU, there are no settings for OC'ing the GTX780, and I can't see an option to "force/enable the discrete GTX graphics" - toggling the ON button for the GPU clock does something, but not enough on my JH, so I am going to uninstall and roll back to the latest Asus GPU Tweak Tool that still supports the G750 without Optimus, 2.5.4.2
Update: After I uninstalled the 1.0.5 version, and installed the 2.5.4.2 version, the application kept crashing and refused to start up... I had to uninstall again, reboot, delete the installation folder, reinstall and reboot again, but now 2.5.4.2 is working ok - Phew!