Yes, sorry for not sharing enough details.
I have LVDS display with optimus enabled. GPU is working through optimus. seems like imac vbios only disables HDMI since after further testing displayport on laptop seem to function just fine.
I am currently running linux. Windows 10 can not boot with imac vbios, just like the other vbios except the ES. I did manage to boot windows 7 but nvidia driver setup keeps complaining about windows 7 being not supported even though I specifically downloaded old version that suppose to. Maybe my windows 7 is too old and I have to update it.
So for now, until I get windows 7 updated, I can only test on linux.
I tested GPU with the plain ES vbios. It worked fine and performance seemed reasonable.
After I tried imac vbios and performance got noticable better, and card was stable. The only notable issue is HDMI not working and inability to boot to windows 10.
After I tried enabling adjustable power bar and set max TDP from 115w to 150w on imac vbios. After this If I set from software TDP limit to more then 100W performance starts to degrade. I tested this with couple games and unigine superposition benchmark.
Unfortunatly linux doesn't have GPU-Z, so what I am planning to do is get windows 7 to work and monitor the card there with GPU-Z.
EDIT: Ok, apparently the only reason Windows 7 booted at all was because vbios got corrupted. ES vbios is still the only one that lets you boot into windows. On windows 7 when any other vbios is installed windows complains about BIOS not being ACPI compliant. Right now I am trying to make modified vbios on my own using ES vbios as base.