CMYK is the addition of color (ink) while RGB is the addition of light. The best way to prove that is because 100% of C,M,Y and K makes black, while 100% (255) of R,G and B makes white. I'd say your best bet is to pick one and stick with it since going back and forth between the two gets very confusing! :) Unless you do like Slynky said and work with one for the filters, then convert when you're all done. I do it that way, converting to CMYK for the color-correction process since I can get a much more precise color management with CMYK. And also not all high-end printers use CMYK, unfortunately. Some really good Epson printers use RGB, as do most color laser printers. But all in all, if you're going to be doing commercial work and taking it to be printed professionally, your best bet is to convert it to CMYK at the end. Good Luck!