ISXP is probably what appears to be the most extroverted to people who know less about types. Mainly because of what WALKYRIA says. They're more extroverted in a wider range of situations, even more so than IXFJs because they will try and get other people to do exciting things with them. They'll be instigating the doing, while IXFJs may only have a few feel-good conversations with specific people. Though I suppose ISXPs might have the tendency to go do a bunch of stuff completely on their own, which would lead to even more isolation than the other types. However based on their "extroverted doers" trait, I suppose that theoretically wouldn't be the case.
In general, it also seems that IXXPs tend to be more extroverted than IXXJs, though that may just be my own experience. Perceivers just seem to get along a bit better with extroverts, we are more open to new and different experiences. We're less focused on habit, and so we're less likely to fall into a routine of isolation like IXXJs. But as I said, this may just be an inaccurate opinion based on my own personal experience. I've never actually read any articles that imply this is the case.