After getting my Saffire Pro 40 Working without the sync problem in Windows 10 (20H2 v2) I was getting awful performance.

Here is a driver hack to get the Pro 40 working just as well as in Win 7:

First of all, get use the Legacy Firewire drivers.

The trick is to use Saffire MixControl 3.7, but with the file 'Pro40Firmware.bin' from MixControl 3.4.

You must then DISABLE the Pro40's playback and recording devices in 'Sound' under the Control Panel. ASIO access to your interface works fine & dandy.

I discovered this hack when I was experimening with the old 3.4 driver and found it worked just as good as when I was on Windows 7, but it was super cranky. I figured something was up.

So I copied the firmware (Pro40Firmware.bin) from the 3.4 version of mixcontrol to the 3.7 version I had installed and - boom. It goes and its just like I'm on windows 7.

I have ~1.0/1.6ms in Reaper and its solid as a brick.

For me, when I want to use youtube etc - I have my motherboard's audio interface going into an input on my focusrite. I also route the Mic to my onboard's 'line-in' jack, which lets me use discord etc. Windows in its daily life never ever sees the pro40. It uses the on-board.