The 750s are designed for short people and ladies. The seats are close to the ground. I'm 5'10" and find it a bit cramped on rides longer than an hour.
The "big-blocks" are more high performance. The 1200 Sport and the Griso put out around 105 hp. I've had a test drive on one, and they are very quick, with lots of torque. Those are the sporty looking ones. There is another 1200 called the Norge, which is fully outfitted for touring.
There is also a line of big-blocks that are based on an older Guzzi design called the California, set up for touring.
When I bought mine, I had my eye on a California, but had to buy the Nevada because the bigger bike wouldn't fit into my garage alongside the car. I've been very satisfied with it, but am now in the process of selling it to buy a larger bike.
There are two basic Moto Guzzis: the "small-block" 750s and the "big-block" 1200s (up from 1100 a few years a go).
The 750s all weigh about 405 lbs and produce around 48 hp, so they're relatively light and agile, handle well, and perform surprisingly well. I usually ride solo, occasionally with my daughter, who is quite small, around 105 lbs, and the bike can cruise comfortably on the highway at the speed limit, 130 km/hr, or around 80 mph.
There are mainly cosmetic differences in the Guzzi small blocks. The Nevada (mine) is styled like an old-fashioned cruiser. I thought it was ugly when I got it, but the looks have grown on me. There is also a model called the V7 Classic, which has 60s styling, and the V7 racer, which looks like an old fashioned cafe racer. In the small bikes, Guzzi seems to be trying to appeal to a more conservative set. There used to be a model called the Breva, which was more up to date in styling, but they discontinued that series a year or two ago.
interesting bike, i am not all that knowledgeable on all the varied makes and models. can you let me in on yours...please.