i really have to disagree with proteal's assessment that the 550 and 750 feel the same, personally. i have both, and they are worlds apart to me, but then again my 550 has new steering bearings, progressive rear shocks, etc. and none of my 750's have been upgraded from stock. i'm also 5'7" and 160#, but this shouldn't make much of a difference when actually riding, and if anything the lighter weight should help. i really wish the 750 felt as nimble as the 550, but it really doesn't. when i get on the 750, i really notice how much power there is at a start compared to the 550, but the trans is clunky and doesn't feel quite as sewing-machine smooth as its little brother. if you've never ridden a 550 around in the 3000-7000 RPM range, you're missing out on the fun and can't really give an educated statement on its power. i wish it had that same snappiness through all ranges though..
as for the 450/550 comparison, it really depends on what you want. i've had a ton of 350T's, but have only ridden a 450T once. it rode well enough on the highway, but any old twin is gonna feel like a vibrating bastard compared to the smoothness of a four. the 450 didn't feel anywhere near as torquey and speedy as the 350 twins to me, but they certainly have a good reputation. if it were me (and i'm not trying to do the same thing as proteal here--you're choosing between two specific bikes..not any infinite possibilities) i'd choose a 350 twin over a 450, unless it was a 60's model. in my experience, the CV carbs can be more of a hassle to deal with when left sitting that the slide carbs in the 550, but on the other hand, they are a little easier to remove for cleaning.
i think you can find 550 for cheaper than that, especially if you are a mechanic, but i don't really know your local market.
