I have erased some of my over-the-top comments and I am writing a short answer really to put Barinder's question back on top again because it was a good question.
My feeling is that Nietzsche is writing an anti-philosophy, and that he would suggest that we humans operate on the level of the instincts. The only check on this would be the true ascetic aristocratic mode of being. The true aristocrat was after land and he was a warrior, not a thinker. Rarely will you find an aristocrat and a thinker in one person, though Descartes had the misfortune of running across one with a very cold library.
Aristocrats fight for what they want, and they satisfy their instinctual urges without any qualms, but this requires a warrior spirit and this requires a fit body, and this may require a somewhat asetic life. We philosophers (who know our Nietzsche) are called to give up our thinking, and our word play to to become this kind of "philosopher-aristocrat", if you will. This is very much Nietzsche's version of the philosopher king, not Plato's.
The second point would be on Descartes' "I", and whether perhaps Nietzsche had studied some Buddhism (idea from Schopenhauer?), and that Nietzsche began to question the idea of the "I" in Descartes (i.e. Buddha would say no "I", no ego, it is not to be found). At any rate, if Buddhism worked to calm Schopenhauer's Will, it would actually defeat Nietzsche's larger project of turning man into an instinctual doer, with the only possible check against the gross display of instinct being the temperament of the true aristocrat (the ascetic, warrior temperament, not a life of luxury and gluttony).
Of course, Nietzsche could not actually "insist" on anything it seems to me, at bottom, his philosophy or anti-philosophy says all facts are interpretations, and this is itself an interpretation...so this is doing, instincts and not thinking, with all the problems and benefits that come along with doing and not thinking.