I just checked a few older issues of the N-Zone to give you a reference for the graphic score.
I found Metroid Prime 3's score being 90 % (SP 94 %), Mario Galaxy's even 93 % (SP 96 %), Zack & Wicki received 89 %, Okami also received 89 %, and SSBB, M&S at the Olympics and Pokemon Battle Revolution all got 86 % too.
Apart from those games, I haven't stumbled over higher scores than 86 % when it comes to graphics. The fact that some graphically rather generic games like M&S or Pokemon received high scores seems to show though that the graphic score isn't too accurate, and it is usually rather in line with the overall score.