I sat on an ST1300 a few times. I didn't even want to ride it after that. It was just HUGE feeling, and very top heavy.
Many people love those bikes, though. However, there is some talk of high-speed instability causing wrecks. Others say it emits tremendous amounts of heat. That could be good or bad, depending on the climate in which you ride.
I would not trade my DL1000 for an ST1300, but I am not you. You may be a bigger person than I am, so its size/weight may not be so unwieldy to you.
Best of luck with your decision. Ride safely.