Is my PSU strong enough?

Firends, family, lend me your ears, for i shall tell you a story of a PSU of such greatness, it cannot be described by mortal words!

Just kidding, i'm just wondering, if my PSU is strong enough for my rig, because i get "AMD driver has stopped working and has recovered" or very rarely BSODs. I had the PSU before getting the new GPU that requires tremendous amount of power.

My PSU in a Chieftec 850W (4 years old)

And my specs:

CPU: Intel i7 920_____130W
GPU: Asus Radeon HD 7850_____450W (allot)
MOBO: Gigabyte EX58-UD3R
RAM: DDR3 12GB of 1600MHz RAM
HDD: a 600Gb 7200rpm Disk
1 CDrom Drive

(NOTHING IS OVERCLOCKED!)

Fans (connected to my MOBO):

-3X 120mm fans (2 are LED)
-2X 200mm fans (1 is LED)
-1X 140mm fan (non LED)
-1X 92mm CPU fan (non led)

Around 4-5 USB devices are alway plugged in. Also my headphones, although i don't know if this is rellevant or not.

One question, does power consumption change when gaming?

Thanks!