Full acceleration may not be on by default. Go to Preferences—>Performance. At the top you should see something like Use Graphics Processor follow by an option selector set to Auto. Change from Auto to Custom. That will give you the option to turn on the GPU for image processing…not just display jobs. When you turn that on below it will say something like max GPU acceleration is now on. This is where having a higher end GPU could start to make a difference in Lr Classic.
It already supported basic GPU acceleration for display. The new full acceleration option is for certain RAW development options. I had to update my graphics drivers to get full acceleration. It's a nice little boost to real-time RAW adjustment, nothing earth shattering though (I'm using a GTX 1060 with 6 GB VRAM).
I had been feeling that Lightroom had either slowed down, or my DB of images was getting too large to handle. In some quick testing this morning, I'm pleased to see a marked increase in speed in moving from collection to collection, or folder to folder, etc. That makes this worthwhile for me.
Don't forget to go into Photoshop's preference for ACR and also setup the GPU to custom so it will work for both display and editing.
BTW, with Lr and ACR not accelerating both display and editing, it could be part of a decision to go for a more powerful GPU the next time you upgrade or replace your machine.
Also the editing acceleration only works with images that use Version 5 (the latest) of the raw processing. You might want to select all your images and then tell Lr to update all of them to the Current Version (V5).