The attack value of this combo, combined with its resilience to attacks from the opponent, make the 17-18 turn baseline much better than it sounds.
It might be even better without cartographer, since with only one counting house you are guaranteed to draw all your coppers whenever you play golem. On the other hand, I definitely agree that an action card with a buy will be useful here, outweighing the downside that you draw fewer coppers. Margrave is nice, but maybe the draw isn't so important, so really anything at all that gives +buy, even woodcutter.
All that said, I worry about the case where the opponent also goes IGG, the IGG and curse piles run out lightning fast, and your opponent has 7 duchies by the time you can reliably play golem.