If I could somehow collect a small stipend every time I answered this question, I could afford to buy these test bikes instead of borrow them. I could also spend more time riding them rather than writing about them. I suspect that some of these questions are motivated by a desire to point to my reply and say, "See, honey, I really do need that 1500. The new roof will have to wait."
If that's your angle, you are asking the wrong guy. Thirty years ago, I rode a 175cc, two-stroke single 10,000 miles through Mexico and never felt badly underpowered. When I returned home, I bought a 350 twin (also a two-stroke), rode it across the country, spending much of the ride marveling at its power. More recently, I went from California to New England and back on a 750 twin. I have also cruised to the sunrise side of the country on several larger bikes. I can't say that I enjoyed the ride on them more than I did on the 350, nor did I enjoy it less. Bikes of different sizes aren't necessarily better or worse, but they are usually different. In the case of cruisers, bigger isn't necessarily faster.