Hi.
I am new in this forum.
Started some weeks ago with SKU.
I used my own house and garden as exersice. Nice.
But suddenly I started up the file and selection was extreme slow.
I found a solution which works since every day 
I created a small file with some basic groups like cube and cylinder. I open SKU now always with that file and selection works very fast.
Next I open my big working file (40 mb) even with lots of textures etc. All works at high performance.
Using desktop.
I5 3570K
Intel HD4000 integrated
2x4 GB Kingston HyperX Fury
SSD 256 Drive.