In case you didn’t see this guide on upgrading AMD microcode yourself.
I’ve been surprised how well my new AMD system works though we are at opposite ends of spectrum of what we want out of our machine. If you do try AMD, I recommend MSI boards. Mine works well. Also checkout renehoj HCL on his 9950x build.
What’s the issue with AMD SMT? Isn’t it off in Qubes anyway? A 9950x has so many cores, don’t think you’ll miss out. My 9600x is so fast and cool, can’t imagine it is using much power