Well Mr. Thick....

You cannot achieve improving kelvin by the method you mentioned. Adding two 2700K bulbs will still result in a kelvin of 2700 no matter how many you have.

Scrog is the one grow I have not attempted to do so I am not qualified to answer about the "hopt for scroing"

Your 400W MH would be just fine for a scrog...it doesnt need to be CFL's.