Seems the first Bios update(F6) was only released, just under a week ago.
http://www.gigabyte.com/products/product-page.aspx?pid=4514#bios
http://www.gigabyte.com/products/product-page.aspx?pid=4514#bios
You hadn't installed the latest Chipset drivers?
Yeah disable onboard gfx, what XMP settings do you get for the ram?
By the way i had issues when upgrading from i7 920 at 4ghz to 4770k but now they are solved it was well worth it as my cards were bottlenecked on the 920 yet even at stock the 4770k doesn't.
just go to gigabyte website and install all the drivers off there for that model mb
your x58 memory won't work aswell on z87,it'll work but not as good as memory designed for haswell
re install the graphic card drivers for your graphic card aswell if you havn't already,flickering like that is usually when your running the graphic card in basic mode as in no gpu drivers installed yet ect