Rikk,
Thanks for being here. I too have noticed a sizeable slowing down after the last update. I could post all relevant info if needed, but basically its a MBP Retina '14, with GT750 and Intel graphic processing, catalog and previews on an external 1T SSD.
When developing, using the gradient filter, clone/heal, brush cause the Activity Monitor show energy use to spike to 400, 500%, stay there for a while. The mac's fan turns on and stays on for maybe 10-15 seconds.
That didn't happen before, and I am sure all things are equal.
I tired a bunch of things, not sure if anything made it better.
In addition, previewing got slower, and, especially, 1:1 zoom got very very slow.
I tried using smaller previews, lower res, etc, and ultimately decided to select a few thousand files I'll be working on and do the Library > Preview > Render 1:1, and keep forever.
Took a while but now previewing is faster.
The developing tools I mentioned above got marginally faster, enough that I don't get too annoyed - but I am almost feeling like getting a new Mac, with its faster processor/cores.
just my 2 cents,
/mike