There is an easy way to prevent this 600mb vram issue with Windows 10.
Disable updates! Yes it's not recommended, but keeping the firewall blocking everything not related to mining you should be ok.
Worst case scenario; You get infected, but there isn't a wallet running on a mining rig, the only thing an attacker can do is use your rig to mine on their wallet, and you would notice that in a couple of days! So no big deal, and if that means you can keep mining eth with your 3GB GPU I think the risk is worth it.
Or you could move to Linux/ETHOS but as you sadi, hashrate will be lower and voltage control is way harder.