The 7700 and 5500 both use octalink v1 spindles so the 118 5500 should work fine with your crank. And you’re right, there really aren’t any octalink options between 109 and 118. Make sure, though, that your FD has enough reach to shift with the longer spindle.
Another option would be going smaller on the inner chainring unless you’re already as small as you can go, which I think is 38 for that crank.