I think the distinction between SP and MP is a bit weird.
I would prefer an unlocked framerate for SP. I don't mind playing games which hover at around 40FPS. Beats 30 anyday.
For me this is a great compromise. I love GG's effects work and they can't do that at 60fps (yet). The SP will likely also be slower paced since they're doing more stealth and open environments. Getting the scale and effects to really show off what the PS4 can do and then making MP as playable as possible is a good move.
I also noticed that the post processing and effects in the MP media is the same at the E3 build of SP which is running and less then half the frame rate. This game is going to be a stunner in both MP and SP. SP for the effects, MP for the fidelity at 60.