Running mismatched GPUs

Mobo is a z590 PG Velocita.
i7 11700k CPU
Main GPU is an RTX 3060.
everything running just fine.

was curious if anyone has had success running a 2nd GPU thats not an exact match to their main?

Ive seen plenty of videos and articles that show it can be done, but isnt working for me.
I have a 1070Ti thats in great condition and when installed as a secondary gpu, I cant even boot to bios.
either GPU by itself boots and runs just fine.

Its not really for gaming, but game design/video/photo editing and rendering, and having multi GPUs can help with vram and task assignment.
the option to send tasks to a specific GPU would greatly reduce render times.
and a combined 20gig of vram would help if I need it all at once.

if anyone has any ideas or thinks I missed something.....hit me up. Thanks.

Thanks for the reply. Im still trying to figure it all out. I have tested the 1070 in another rig and know its good. even swapped it in this one and ran it solo to hit with benchmarks and such.
But when both are in, black screen. if I could only get past that!!!!
Just would be cool to have a 2nd GPU for rendering split tasks.

Interesting thing, slight chance I may get my hands on a 2nd 3060......just hoping if thats the case that it also doesnt end up with black screen when trying to run a matched pair.

also appears I need to get an SSD to run Starfield, so theres that hurdle ahead.