Well, curiosity got me and I pulled the trigger on the BIOS update. On my last attempt to get something out of ASUS support, they told me this new bios does NOT patch the meltdown/spactre vulnerabilites, so I decided to push the button.
No performance difference as far as I can tell. Same scores in 3dmark, heaven bench and Cinebench, but I noticed the CPU now runs a little bit cooler, like 5c less then it used to and the temps seems to not jump up and down too much like before. So now the GPU also runs a bit cooler (both are connected to the same heat pipe) in games. I still don't know what exactly they have changed, since the clocks, voltages and everything else seems to be the same. I'll investigate more.
Also, meltdown/spectre is indeed not patched. Checked it using InSpectre. I don't really see that as an issue.
No problems whatsoever, rock solid stability and slightly better temps. I'm giving this one a thumbs up.
