Ok, just a mini update as to what is happening.
My Ram: https://www.gskill.com/en/product/f4-3466c16d-32gtzr
After hours of my time playing around to get the RAM to post it turned out (very rare apparently) that one of my G.Skill modules was faulty as well so I returned it as DOA and got a replacement. I came to this conclusion by removing one stick of my RAM and testing with one. One seemed to work ok managed to post and boot into windows, was able to say play games and what not safely as well as passing the windows memory check. The other stick however had a multitude of issues with BSOD, unable to post, and constantly crashing and failing windows mem check.
Got the replacement RAM today and I still haven't managed to get it to post with XMP enabled, on the advertised speed of 3466.
After some time of tinkering, I gave up trying to even get it to post... This was predominate done with tweaking the IO/ SA/DRAM voltages... even losening the timingts from out of the box 16-18-18-38 to 18-20-20-40 (still no luck)...
I decided to look at everything again and back to the 'XMP baseline profile' (IO/SA AUTO) and take a diffrent approach. Loaded a slightly higher DRAM voltage 1.36v, set a slightly lower clock speed one of which is 3333mhz with the out of the box timings of 16-18-18-38 such as: https://www.gskill.com/en/product/f4-3333c16d-32gtzr
as well as it being identical timings to my purchased model.
Magic it posted... booted into windows.... huurah....
Having a quick look at HW info here are the following voltages I've noticed;
DRAM: 1.36v (i might try to lower this back to default 1.35 set manually).
VCCSA: 1.272v (auto)
VCCIO: 1.312v (auto)
Interestingly the SA/IO voltages are a fair bit higher than I expected when applying manual voltages to get it to post at 3466... I was in the range of 1.20 - 1.22v... Maybe I'll try that voltage ranges at one point manually to see if it can post/boot.
Yet to do some memory stability tests but at least it boots its a start... A little disappointed that I cant get it to post or boot even though the g.skill site clearly lists it as compataible with the z370-g... https://www.gskill.com/en/product/f4-3466c16d-32gtzr#tabs-qvl
I'am hoping future bios updates might be able to resolve this and or even improve better compatibility.