You actually are always printing at 2400*2400 DPI, because that is what the printer does by hardware.
What you see in the driver is how the jobs are interpreted and ripped.
So the Fiery takes your job and renders it according to the resolution dropdown (600 or 1200) Obviously file size changes massively dependant on which you choose. 1200 is great for text (crisp), 600 is great for images (colors,gradients,saturation). Color issues can and do occur at 1200 as can be seen here, not always, but often enough.
And here is where the real difference is noted. 1200DP does not equal 1200*1200DPI, they are entirely different measurements.
1200DPI is the amount of dots used to make a digital image appear on screen total within one inch.
1200*1200 (In the C75 it is 2400*2400) is very different, in the CMYK world, unlike the RGB, you divide resolution by the toners.
So with this CMYK device you have the 4 colors, so you divide 2400*2400 by 4.
So each color (CMYK) prints 600*600 DPI, when all 4 colors are laid down, there are 2400*2400 DPI.
I have had this press for close to 3 years and have asked that question so many times, and you gave me an answer that makes sense. THANK YOU THANK YOU THANK YOU!!!!