You should in no way be worried about your psu with only one gtx 780. They will run on as low as a 550watt power supply with no worries at all. A 700watt powersupply leaves you with lots of room for overclocking even. Corsair hx, tx, and ax series psu's are all very good and reliable, not to mention they run very cool; but you should be more than fine with that psu anyways. The it looks like the numbers you are looking at are actually the fancurve AND temp for the graphics card, not the psu (takes some different software to tell you about those numbers).
Anyways, with the 780 having such a good reference cooler, you should only worry about temps or fan curves if:
1. You find the card is running over 75 degrees
2. you find the card is running louder than you would prefer.
Hope all this helped, and feel free to ask any other questions