Although I installed a BT45 on my ST1300, I regret that choice and will go with the rear Activ in the future. I've run 4 of them on the front of my other bikes, and have gotten 34,000 happy miles of even wear from it on my 93 Goldwing, less on the Valkyrie.
https://www.amazon.com/Michelin-Pilot-Activ-Motorcycle-Cruiser/dp/B005J87XCG
The BT45 follows lines and wallows more with road flaws than the Activ. I do run them in the reverse arrow direction, but did not do so with the BT45. 42 psi in all of my tires, btw.
I only have about 6500 miles on the BT45, so I reserve the right to change this opinion as it wears. I'm also new to the ST1300, so other's experiences carry more weight. I'd like to hear opinions from any other Activ users (rear tire on front).
I use 4 oz. of air-soft beads for balancing /stirs pot/.