Holy shit, I just learned that if you completely turn off 3D in MH3U (not just via the slider, but actually disable it in the main menu options), the framerate improves. (More or less noticably, depending on how sensitive you are to framerate.)
That option is also in MH4U, right? I hope that since I (a) don´t like playing with felines, (b) don´t really need the 3D effect and (c) exclusively play solo, the framerate will be a lot smoother than in the demo on the old XL.
Oh, and considering the camera options: Since MH3U was my first Monster Hunter I got used to the lock on cam right from the start. I personally think that the big plus is that I can stop thinking about the camera and instead focus completely on myself and the monster.
Another plus is that I never have to lift my right thumb off the attack buttons. I tried the CCP on my XL some time ago, and having to switch between camera and the face buttons got really old quickly.
I tried getting into MHFU on my Vita, but even with a really good second analog stick, constantly having to bother with the camera is something I never got used to, and it really hindered my enjoyment. (I totally understand that this is personal preference, many players who sunk thousands of hours in the pre-lockcam games will definitely prefer it that way.)