Hi - thanks for the reply.
I suggested the UCX route to the devs but they said that using that still essentially uses a complex collider mesh rather than the simple one so would be less performant (although if 100% i could use them)
Regarding the collision editing tools - ive never actually used those before - is that to edit the collisions on a per instance basis? Im basically going through every staticmesh file and setting the collisions there so am looking to make changes in the staticmesh viewer really.
Thanks for the info on hiding the environment - that did the trick 
thanks again for the help
Nick