New graphics card

[Gamekiller20]

I am considering to buy a GTX 980 but I have 2 questions.

What is the difference between the MSI GEFORCE GTX 980 4GB GAMING 4G and the Asus STRIX-GTX980-DC2OC-4GD5 4GB DDR5?

Right now I'm using the Asus GTX660-DC2O-2GD5 with my 450 watt cooler master RS-450-ACLY power supply and I never experienced any problems (the card uses 150 watt), but the MSI GTX 980 uses 165 watt and I've heard it needs at least a 500 watt power supply.
Is it possible to use the GTX 980 with my RS-450-ACLY power supply?

Edit:
Intel Core i5-3330 3.0GHz Quad-Core Processor 9W - 77W
Asus B75M-A Micro ATX LGA1155 Motherboard 15W - 60W
Crucial Ballistix Sport 16GB (2 x 8GB) DDR3-1600 Memory 18W - 18W
Seagate 2TB 3.5" 7200RPM Hybrid Internal Hard Drive 4W - 20W
MSI GeForce GTX 980 4GB Twin Frozr Video Card 41W - 165W
Total: 87W - 340W
Al sites say the 980 needs at least a 500 watt power supply but pcpartpicker says a 450 watt power suppy is sufficient

 

[PP Mguire]

Well you kinda missed the most important part, what IS your PSU?

The difference between the two cards would be the cooler and PCB. Otherwise essentially the same thing.