Thanks for the word up Elsksa, I have to review my keywording, missed this one.

Got in touch with support, which I should have done from the get go. Very quick to answer, big up to them. Pasted below in case someone ever wonders about this.

yes, you can use both RTX 2070 and RTX 3090 together ...

Hi all,

I'm looking to upgrade my graphic card from an RTX2070 super to an RTX3090 24gb. I was wondering if there is any point in running both card together in the same unit or just use the RTX3090 on its own.
I looked at octanebench page but slightly unsure about the meaning of: "varies by cards ...