I'm a female INTP dating a male INFP. He is the only INFP I have known well (I think), so consider this a "case study" more than aggregate evidence. A few observations from my end:
My INFP is not only more willing to communicate his feelings, it is obvious that he knows what they are (I am often confused about what I feel). He is also quite articulate in expressing those feelings, in a similar way to how INTP like to be very exact in their descriptions (except of feelings).
More specifically, I notice the differences in dealing with people. My INFP has a really hard time being in a "disciplinarian" role. He *thinks* he is giving criticism but it comes out very gentle because he really doesn't like conflict or hurting others. I am way more likely to be harsh on someone that deserves it, not to be mean, but because I think people who are screwing up need to know it. Their feelings enter in only as a secondary consideration (i.e., I don't want to create enemies).
While his intuitive sense of people can be very good, his optimism/dislike of conflict can lead to seeing only the good (or non-existent good) in people that honestly kind of suck. This has happened several times. Even after, in my opinion, someone has revealed themselves to be untrustworthy/selfish/dishonorable, my SO will have a hard time cutting them off. He tends to feel sorry for them, while I tend to write them off as lost causes with no shortage of contempt. He has in the past been very guilty of trying to "fix" people. I think the INFP is about the least likely type to fail the "would you have been a nazi" test, because they see what is human in everyone. It can be endearing but also maddening, and I have to stop myself from trying to "protect" him from worthless people that waste his time.
Another differentiating scenario would be a crisis situation. In general, I will go into robot mode and start doing the "logical" things (call 911, do CPR, whatever). My INFP tends to freak out. Not to say he will be useless but it's clear that the emotional side of him is very active, while for me it is even more suppressed than usual. On the other hand, if the crisis is not "someone cut their arm off on a table saw" but two people getting into a fight that might become physical, the INFP is probably a better person to have around, as when he wants to he can be very manipulative (i.e., to alter the emotional state of the combatants) to achieve a better outcome.
Anyway, hope that helps.