Relative sugar content of liquors?

Speaking of the Cooking Issues blog, their post on agave nectar vs simple syrup got me thinking. They were comparing the two, and part of the process involved using a refractometer to determine exactly how sweet each ingredient was in order to normalize that variable during the taste test. So I was wondering if there existed somewhere a reference where you could find out the sugar content of liquors. I poked around, but alas, google failed me.

I'd find such a reference useful when tinkering with recipes. Say, for example, you wanted to swap some of the vermouth in a manhattan with Benedictine, or some Cointreau for Chartreuse in a margarita, but wanted to maintain the same sweetness. We know the alcohol contents so at least we know what's going on with that, but with the sweetness I'd at best only be able to tell you which ingredient was sweeter, certainly not by how much of a factor. It's not so bad if you're dealing with a simple swap, but if you're striving to create something with several sweet ingredients it can get messy fast. Or maybe such info would be cheating, I don't know.

Not that the trial and error's not part of the fun, but sometimes it would be nice to have a better idea of where to start.