I think that the ones we have on here currently for Game Maker 5, 6, and 7 are all just edits to the images used on the Game Maker Community. These edits being to remove some of the anti-aliasing so that the icons we use look alright on a darker theme, and the edit to the Game Maker 7 logo also consisting of a color change likely so it'd be able to be seen easier as well.
Your image is alright, but it doesn't have the "G" thingy in the middle of it; and the 8 is too "boxed" - the corners in the GMC image are "rounded". It's cool though and you're right we should get a GM8 logo up sometime sooner than later.