I've heard so many people talk about how fast LR 6 (CC) is. For me, it's been a dog. I'm on a Mac Pro just two years old with a fast video card as I do a lot of video editing.
Once I've imported a folder of pics into LR6, culling is dead slow. I'll click on a pic while in the Develop module and wait for it to appear. I click on the sliders to make changes and I just wait and wait. Seriously? I'm falling asleep trying to cull a couple thousand images. Do I really have to go back to LR 5?
I'm one of the people who talked about how fast it is. BUT after a few solid hours of using it I'm noticing that the interface is still unbearably laggy. Certain things quicker, gradients for example. One thing that was unbelievably slow for me today was waiting for it to draw a 1:1 preview - it took a minute from a d800 raw file (and it was doing nothing else). Other times its taking ~15 seonds (twice as long as previously). In the develop module it takes 4-6 seconds before I can edit an image.
In the meantime my system has gone from a xeon x5650 to an i7 960. I expect things will speed up again when I reinstall the xeon.