Glad you find the VTX 1800 comfortable. I think however as far as engine size, you may be forgetting the Triumph Rocket 3, 2.4 liters of grunt.Their largest ever motorcycle engine that isn't a flat-6. Was offered in 1/2 dozen+ trim levels, so something out there for any taste. Prices on the used market for the 1800 is comparable to what you'd pay for similar condition NTs.
Mike