An F20C head flows more out of the box then the k20a. It variable valve timing isn't as good though. Take a f20c, long block, throw in a k24 crank, and appropriate rods and you will be making around 240whp. The stock f20c pistons are forged. The K series and F series share a ton in common in their design. Same bore spacing. Similar cylinder head design.
Inline pro has made 300whp with a 2.7L k series with stock head, intake manifold, header and throttle body. These motors are very potent.
To each their own. Regardless you would have a good amount of money tied up in building a f20c. Might as well do an ls1 if its all about hp/dollar.
Justin