Wow, I am really glad that I checked this, lol.
I am one of the leaders of a largeish (16+ which is a lot for that kind of shell) social LS, TheReturners. Really a wonderful bunch of people, almost always someone ready and able to get up and help someone new to the game. Lots of small grouping for events.... our shell in particular doesn't specifically do endgame events persay, however within our shell we have several leaders of specific event LSs including Abyssea, Dynamis,and Salvage. Its really nice since you will be doing these events with friends from the shell.
I was pretty excited also to read you were possibly interested in RP. Its a bit of a dying breed on XI, but I actually run the RP LS on Siren. We are one of the few groups able to say that we are still growing, with over 10 active members. Been going for around 2 years. RP experience isn't necessary and we do lots of missions surrounding the game's mission storyline, so if you want to get into the game's story and also make mission progress, head over to
HTTP://vanatales.8.forumer.com. Make an account, look around, ask us questions, we are a friendly bunch.
Downside to Siren that I will tell you of now. Until the version update (May) server is closed for character creation since we are being merged. But if you can hold out a month, I am pretty sure you will find what you are looking for.