Both are rare, if you're both happy with the trade and you both want it, do it. The whole min-maxing trades that is done so often just ruins the community, IMO, since you always have people trying to take advantage of others.
So, the end question, are they both rare? Yes. Are they both rarely traded caps or caps that, when sold, sell for way too much and around the same price? Yes. Would you be happy with the cap you got from the trade? If yes, make the trade and stop trying to get more for it.