What the GW77 lacks relative to the 760:
1. Any ability to add an extender lens (but it does have the 17X extended zoom).
2. No focus dial (but it does have manual focus).
3. The stabilization is not as good as the 760, but better than the SR11 and excellent.
4. No manual control of shutter (but it does have manual exposure, wb, and focus).
5. No external mic input.
6. No 5.1 surround audio (stereo only).
7. No viewfinder.
8. 16GB internal memory versus 96Gb for the 760.
9. No ability to screw on filters (but there is a filter solution).
10. No direct copy from the camcorder to a hard disc.
11. 26mm versus 29 mm for the GW77 at wide angle.
12. No video light (but there is flash).
Of course, the GW77 weighs almost one pound less, with battery, and is pocketable and shockproof, waterproof and dustproof.
And, yes, the extended zoom feature also works with any optical lens extender and so multiplies it.
The Sony CX580v costs $100 more than the GW77, but it has 5.1 audio, the ability to add filters and lens extender, external mic input, direct copy, 12X optical, 20X extended, 32GB internal memory, and video light.