Well a 550 will have less than 50 HP too, especially an old tired one, so that's not a real powerfull bike either. I've been on a 400 a few times, and it's doesn't feel a lot less powerfull than my 550f.
Let's face it, these are old bikes. They will never be really powerfull compared to a new sportsbike. I like the look of the 350f more than the 550f (I think it's the tank), so it would be a great start for a cafe. If money is not a problem you can get more horsepower from that little engine too.