HW Vertex shaders should always be ON. This was a feature added back in the day when video cards were pieces of shit, this allowed the CPU to take up some of the load to ease up on the video card. Now that everyone has a "recent gen" video card, the video card can actually process this better than the CPU can, so you must leave it on.
This has a side effect of bottlenecking your RAM too, because anything that goes thru the CPU must also go thru the Ram. So by making sure every single one of your clients has HQ Vertex shaders on, you should see less CPU and Ram consumption overall- usually about 3-5% CPU usage per client you have loaded. You'll probably also want pixel shaders 2.0 on there, because video cards process this better than forcing them into a legacy mode from 15 years ago.
I recently did this as I was pegged out on my ram (16gb running at 90% usage) and after changing this it drpped down to 50-60%, and thats with 14 characters.
If this helps ya, please hit thanks......thanks!