Federer's had tougher draws than this, that is for sure. Anyway, any RG final that includes Nadal is instantly tougher than any opponent Federer will face in a semi/final of a hard court major, so you are off base to begin with.
I agree about it being a very difficult semifinal, but in terms of finals, the French and Wimbledon finals of the past couple years have proven the most difficult for him, especially since those majors seem to hold more emotional value to Federer.
I see it as a foregone conclusion that Nadal is in the final. Tomorrow night will be very interesting.