I think we have to look at what a droid can't do rather than what G0-T0 can't do as he is very intelligent. But as a droid with a droid army he must have weaknesses e.g. ionized particles - but whether Plagueis can exploit those weaknesses is another matter.
It also stands to reason that G0-T0's body would be more resistant to ionized particles than most other droids. If we look at what a droid supposedly can't do, I think we're making a huge mistake. As a droid progresses without memory wipes, they develop more and more of a personality. While they may have a core objective, they also can have free reign on how to accomplish it, and then we have droids that completely surpassed their programming. Is there things G0-T0 might in theory overlook, sure, but any organic (for lack of a better term) could also overlook things.
Thinking Darth Plagueis has the advantage simply because G0-T0 is a droid, is a serious mistake; especially since G0-T0 had already outwitted numerous other crime bosses on a routine basis.