If you do that i7 probably won't work at all or if you manage to boot you will have stability issues and other problems but i'm 99% sure that you won't even be able to boot.
So your best bet is to install newest BIOS.
Nothing bad will happen if you do it right and make sure to have stable electricity because if you lose electricity your update will fail.
I have done dozens of BIOS updates on multiple motherboards and never had a problem.
That is a very early BIOS, so yes you will likely have to update it to support the 4790k.
If you follow your manuals instructions to the letter and the area you live in is not prone to power outages there is very little risk. Page 3-54 onward. That board has ASUS Crash Free so it's very unlikely you will brick it even if you screw up the BIOS update, that board can flash a BIOS without even POSTing.