Not noticing anything like that here, images change pretty much as fast as before.
In fact, after some use over the last week, I'm seeing the develop sliders being slightly more sluggish in response.
W7 32gb ram 3.9ghz i7 separate SSDs for program, catalogue and files, GTX470 3840x1440 desktop
Same for me, Win7 64 bit, SSD for OS and separate SSD for Catalog. 32GB ram, GTX970 4GB.
There is a bit of a speed boost, maybe 30%, but I am still not seeing anything really hit the GPU, (per the Asus monitoring software) where as with Photoshop CC, you can see it hitting the card. So it seems to be all processor and memory working in LR. I will take the 30% for sure!!.
Still seeing a strange lock up, that I started getting with the last version, where with the adjustment brush, it freezes momentarily while drawing with the brush, then it tries to catch up, but then all the ensuing brush strokes are black, and the program locks up hard. On reboot, the existing adjustment brush icons no longer show up, and you have to go back and turn that feature on.
I am not using Smart previews and on average I will have 8 or so adjustment brushes in a file, (most of my work is now done in LR) very little in CC, only topaz clarity.
Paul C