I have a PC which can run the game at 1080p with all setting maxed out with a FPS which varied from 40-55

Would i be better off capping the FPS at 30 or allowing up to 60?

Personally, I'm OK with playing games at 30 FPS, but there is a noticable difference to 60 FPS. 60 is just smooth as silk and if there is any chance to achieve it without making the game look like crap, I would go for it.

My suggestion would be to lower the Foilage Visibility Range from "Ultra" to "High", as High looks almost as good as Ultra but it saves quite a few of FPS, and I would disable the Hairworks. I think default hair looks good enough as it is, and Hairworks will again cost you quite a few FPS.
With these two changes alone you might already get close to the 60 in outdoor areas.

I usually also lower shadow quality because I don't really need pixel perfect shadows.

I have a GTX770 2gb, 4690k and 8gb ram. I can run pretty much locked at 60 after disabling hairworks, dropping shadows to medium and reducing foliage distance to medium.

If a little bit of pop in bothers you and you MUST have sharp shadows, locking to 30 is really your only choice. I prefer framerate over pop in, but it's down to personal preference.