Change of Saddle

They say you need to give yourself time to get used to a bike seat. I'm sure the original one fitted to my bike (pictured coming off) is very hi tech and engineered for efficiency but there's no getting away from it, its pretty slender and hard, and upon nearing the end of my longer rides the numb backside rather than loss of power in the legs is the limiting factor.

I was working at the desk today and went for a ride at "lunch hour". I was sure I would beat my PB for the Cour round which is about an hour and 12 minutes and today I was an hour 12 minutes and 24 seconds (obviously I worked on later in the evening to keep my time sheet right).
This circuit is very rough in places, which limits speed, and I had to go through the muddy section where last I fell off and there are four gates to open and close. I'm trying to think of more excuses. I even thought I was going faster with the change of saddle.