What's the worst that could happen if the bios flash doesn't work right? Will my card be dead? And I am going to have a 690 as my main card, with three 7970s for mining. Is there any way I can accidentally flash my nvidia card with the AMD drivers?
The worst that could happen would be you would brick your card, unlikely but possible. But if the BIOS didn't work, you should just be able to boot off another card and re-flash the BIOS.
You could accidentally flash it if you didn't put the correct device number in the flashing utility - If you are worried about that just take it out when flashing.
It's up to you, i'd do it, but i do take risks with my tech sometimes..