Is there any reason why the video out from a GoPro be used as the primary FPV feed? I haven't seen anything about this and most folks seem to have a separate camera dedicated to FPV.
I could go for the higher power Tx - I do have a Ham licence (G3... & ex ZL1...)
... it looks like 25mw is the only legal transmitter power for 5.8GHz in the UK. The specific wording is around the use of "video" transmission - so although a Ham can use higher power on 5.8GHz, they cannot legally do so for video [specifically].
The only exception to that being equipment that is within 25mw on 5.8GHz.
Donald, reading this thread, can't help but think that you are almost there with your solution. You can just take the live out from your gimbal and either route it through the iosd (if you have one) or simply to a vtx. The great debate is whether or not to rely solely upon the gopro on its own,or incorporate a second dedicated fpv cam in your system.but as you have indicated that you do not need fpv per-se, the gopro and line of sight would be enough would it not?
As one senior officer once told me on a different but similar situation: "It is a matter of the spirit of the law rather tan the letter of the law." Common sense prevails (most of the time, especially when the 'jobsworth' is on leave!)