upgrading a mac? Are you sane? I heard it's perfect so no need for hardware changes.
I love imperfection so I use Windows... Linux should be better but no Sketchup.
I can tell you that, with windows, changing from a laptop with an nVidia 425M with 1Gb to a Titan X with 12 Gb, simply changed everything I knew about LO and SU.
I feel it's a different software, and though it has limitations, performance has increased so drastically I cannot conceive how I could cope with it.