I was under the impression that to calculate the amount of Amps needed on the 12v rails you took the total 12v current (in this case adding 18A and 17A to get 35A).
Then you look at the total wattage required to run just the GPU (usually under full load) and divided that by 12 to get the amount needed on the 12v rails to adequately power the GPU.
The total wattage the TWIN FROZR II according to the below article is 157w under full load.http://www.techpowerup.com/reviews/MSI/GTX_560_Twin_Frozr_II/21.html
So dividing 157 by 12 we get 13.08A necessary for the GPU alone.
i5-2500k TDP is 95W/12 = 7.92A
Lets add 5A to be in the safe zone.
Finally add in motherboard power draw, RAM, hard drive...it's about 1A-2A, but make it 3A to be 200% safe.
Adding all that up we get 29A on the 12v rails required to run your proposed setup.
Considering that your PSU has 35A on its 12v rails, you should be fine.