I think you need to rent or borrow an 1800 and ride it for one day. At the end of that day, you will go buy the one you are one, or find one that you can buy.
I had a gl1500se and loved it very much. I traded with a friend and rode his 1800 and covered 250 miles by the end of the day.
My next bike is going to be an 1800.
Better balance, feels lighter and lower when stopped.
Brakes are eons better, the ABS is debatable but I would opt for it.
Pillion seat is the best of them all, and if she is happy, I am elated
The headlights at night are the best ones I have followed on a bike, including add on driving lights.
You loose on some things.
Foot/leg comfort if you have a long set of legs. I am 30" inseam and felt fine though.
Lack of storage space. Learn to pack lighter or pull a trailer.
Costs more. Oh well, depends on your wallet.