Now that I've had plenty of time with Lr CC I can say that the time necessary to import and create standard Previews is dog slow. I don't have any benchmarks but I'm confident it's a LOT slower than Lr 5. I'm often importing 700-1500 images. This is on my Mid 2011 iMac with 16 GB RAM, quad core 2.5 GHz Intel i5. I disabled the GPU performance enhancement because it was slowing down editing with the brush, radial filter, etc. Sigh.... I guess I know what I need for Christmas.
On a positive note it's faster on my Retina MBP.
