I had the 3" extender on the lower ram-ball mount (2nd picture you show), but they didn't work well together at all. You couldn't really see the GPS with the tank bag on when riding easily and you couldn't really touch the screen easily either (this was adjustable, of course, but it didn't really make it any better). In addition, if you lifted the GPS up any higher, it interfered with being able to see the speedometer, so they don't go together well. It might work if you can get a 5" or 7" extender and push the GPS off to the side of the bag (with the extender at an angle), but I don't think it would be that much better.
I think, if you have the tank-bag, you need to either mount the GPS in the triumph GPS mount location, or on the handlebars off to the side (not the center).
I can say the tank bag and Triumph GPS mount/location work well together, but it is a pricey solution.