We had very similar setups..
I've had several Autocoms (laterly the SPA)with Garmin 660/BMW Nav 4 and 5. Used as pillion intercom, make phone calls, navigate, listen to music and chat to other riders with a PTT. With the Nav 5 I added the Autocomplete BT unit.
The Autocom was excellent with clear signals, except on the iPhone 6 and I loved them as they were far superior to BT offerings years ago.
How things have changed...
I took the plunge after reading all I could and bought a pair of Sena SMH5. I haven't tried every model of every brand of BT headsets so can only talk about this unit but...
What a difference! No cables, except my in-ear ACS Pro 27 communicators [superb protection and sound], which are really easy to connect (use a 2-3 inch 3.5mm jack plug extension to make it even easier and prevent wear on the expensive bits). When I was in France (where in-ear buds are banned), I reverted to using ear plugs and the Sena speakers and they were excellent. The build quality of the units is also excellent.
My setup:
My BT connections are to my Nav 5 for music, navigation, telephone calls, safety camera alerts and directly to my mate using the Sena BT to his Sena set.
Range:
The BT range is line of sight up to about 500m. In sinuous roads in mountain passes, you have to pick your moments to chat, but that's the same with FM.
Battery life:
The units last several full days if you're only connected to the Nav 5 and all day if you're connected to another set.
Although they have a safety feature that they temporarily close down if soaked, we've been soaked and they haven't shut down. I expect an ice bucket challenge might do it (anyone doing that, tell me how you get on).
Tips:
Sometimes my "device" (the music), isn't found, so turning the Sena of and on again solves that. I think it has something to do with the order the BT units connect.
My mate and I kept dropping connections, each time a speed alert bonged,but once we turned off the speed alerts in the Navigator 4 and 5, the connections were solid.
I would have no hesitation recommending the Sena SMH5. I'm ordering and 2018 R1200GSA with the TFT screen and connectivity.I'm hoping that BMW haven't done anything 'trick" to the open source BT connection which might prevent me from using the SMH5.