Or 'cycle ergos' as our American chums like to say.
Here's an interesting site. You put in the bike you are interested in and a few details about your size, and it tells you what your forward lean angle will be, and the angle of your knee, which are the two measurements crucial to comfort. You can put in two (or even more) bikes and compare them in a nifty graphic that fades between one and the other by rolling the mouse wheel. It's very clever.
I'm not too sure about how accurate it can be, based on so few parameters (height and inside leg), but it's certainly interesting. It tells me that, by moving from the Bonnie to the Sprint, I will be moving from upright (0°) to a 25° forward lean, and my knees will be bent at 81° rather than 82° - a slightly more acute angle. (That's not what it felt like while actually riding the bike, but we shall see.)
Warning: motorcyclists, especially those who have a few bikes in their history, may waste hours of precious time on this site, and learn nothing they didn't already know. You have been warned.
Here's me on the Sprint:
and the Bonnie for comparison:
The positions in the two pictures look about right, from the 'feel' of the bikes. As I don't go around looking at myself in shop windows (I don't like to mock the afflicted), that's the best I can say. I do think the Bonnie rider needs a pipe, a cardigan and possibly a trilby, though.