Why is shift-control-q so slow sometimes? 

Today, I've got a 20 config part that I could have clicked through each config faster than the shift-control-q worked. Assemblies are particularly slow, and it seems like it gets exponentially slower with each added configurations instead of linearly slower. 

Other times it's lightning fast. 

Also - as someone who works extensively with configurations, I advocate for some sort of "rebuild selected" feature! 

I'd love any insight, because I prefer to shift-control-q before I check a design into the vault. 

Thanks!