I just installed Lightroom 6.0.1, which is an update to fix a couple of bugs. It doesn't seem to offer any performance improvements. My impression is that LR6 is definitely slower than version 5. I'm running it on a new laptop with a compatible GPU enabled, and I also have a fast SSD for the program files. My images are on an external drive, as has always been the case for me. Maybe things will get better with subsequent updates..? I've tried the program both with and without the GPU enabled, and it seems to make no difference. I'm not doing any scientific (or even unscientific) tests here... just completely subjective.