I've tried tweaking my system to improve performance many a time but nothing has made much difference. My system/usual tweaks are:
* RME UCX @ 48khz with MMCSS for ASIO enabled
* i7 4790K OC'd @ 4.4Ghz with the usual recommended tweaks for music production like disabling speed stepping etc
* Cubase settings: Multi-processing on, Normal ASIO guard on, Stenberg Power Scheme on
* Windows tweaks like optimising processing for background services and disabling any other unneeded programs etc from in the background as far as possible.
I was never all that happy with the performance though and just put it down to me favouring powerful plugins and softsynths. (Omnisphere 2 and certain Kontakt sample packs can be pretty demanding for one but I always need them), but today after I had crackles on my default template at all buffer sizes I went and did some more tweaking to my usual.
The first was enable Audio Priority in Cubase (I think i've tried that before though and it made no difference), and the second was changing my graphics card setting via its control panel tray icon from Graphics Profile - balanced, to Optimize Performance. (I use an aging gaming card, AMD R290)
I then double checked my BIOS settings and everything was the same as usual for my modestly OC'd CPU and with the usual audio performance tweaks in place like disabled speed stepping etc, but when I rebooted and started up Cubase with my template I couldn't believe the difference!
The performance meter with nothing playing had dropped 50% and I was able to play at 96 buffer no problem whatsoever. In fact I could get it down to 48 and play all my hardware synths no problem but once I started adding much more in my DAW insert wise for example I always had to increase that so 96 is my new 'normal', but it's nice to be able to play at 48 without compromises on my default template.
So, the key thing that I had never tried before was changing my graphics card to optimise for performance, and possibly boost on Audio Priority.
It's not an audio production system optimisation tip i've ever heard before in my 20 years at it, but maybe most people are just using onboard graphics for example so it's not an issue for them.
Anyway, I hope this helps someone else out.
[Win 10 x64 (not the new Creator release), Cubase Pro 9.10 x64]