I’d have to go with the 750 for the reasons others have stated plus I have an original 75 550 f.....I’d like a 750 however and that one looks real nice.
....btw, it looks like the end of the muffler on the 550 is black, or just the picture, I can’t tell. It should be just chrome..and the seat should be a dark brown, hard to tell ....If not, maybe you could use this as a bargaining tool for a lower price on the 550....good luck with your purchase.....and looking closer, it looks like incorrect handlebars?, or just rotated up ?