I never liked how vBulletin clumped all posts together. I really enjoy how SMF and IPB distinguish between someone's posts and created topics. It makes it easy to find a specific topic if you know the creator's name but not the title ("I remember this one topic about ponies started by mahz, but I can't remember what it was called..."). 

Since you already have RPs treated differently than normal topics, it makes sense to have a filter to see RP posts vs non-RP. I'm not sure whether it's better to clump IC and OOC posts in together or not, though. 

As far as the UI goes, I rather like seeing the About/Overview page first when loading a profile. Even if there are other options, the typical reason I visit a profile page is to learn more about someone. When did s/he join? How many posts (total) do they have? Some biographical information, if they've revealed that. Maybe some stats, like where they post most often, when they were last active, when they joined (exact date, not fuzzy time), etc. 

I'm not a big fan of tabs, but it does follow the UI scheme you've already created here. I say go with that. 

Also, I currently really enjoy the quick way to see which PMs I have with someone already, but that box does take up space if I haven't PMed a particular person yet. Maybe that could be expanded on to topics (and broken into RP and non-RP sections) where you and this person have interacted before?