UI Speed issues

Does anyone else have problems with the UI keeping up with mouse clicks and draging elements? The whole UI feels laggy.

I run a two week old install of OS X 10.11.3 on a:

Mac Pro (Mid 2010)
2 x 2.4 GHz Quad-Core Intel Xeon
48 GB 1066 MHz DDR3 ECC
ATI Radeon HD 5770 1024 MB + NVIDIA Quadro 4000 2048 MB
Samsung SSD 840 PRO Series 512GB

The usual suspect for sluggish UI in Motion for me is having motion blur active in the viewer render settings. Switch it off, go to half rez and draft processing and I've got a rocket.
Editing anything that requires the realtime cache to be trashed and rebuilt from the beginning, replicators and particles and such, is going to sow you down,
There are many ways to improve the performance of Motion when editing but I don't know how many of those you've tried. You've certainly got the Mac and RAM to handle just about anything (assuming you're not trying to apply massive alterations to 8k footage that has to be decompressed on the fly).

Standard disclaimer: The wonks will be along later to correct my misperception of your situation.