This isn't really on-topic for "motor vehicle repair", but I figure it's kinda close.
A few months ago, I bought a 1983 Honda Nighthawk 550, which has a straight-four engine. A friend of mine was looking at motorcycles also, but ended up buying a gently used 1800cc V-twin. I went to the dealership with him and asked what size he should look for to compare to mine, and the guy said mine would compare to a 1100 V-twin.
I'm curious because he was a commissioned salesperson and may have been trying to upsell my friend, or he could have been right. My dad also rides and has a Kawasaki KZ900, and sitting on it, it feels a LOT bigger than mine.