If it's like my C44, the DPI settings map to Economy, Normal, Fine, Photo and Photo RPM - visible in "Advanced" and some are dependent on certain media - Photo RPM is only available for Photo paper.
I believ for mine it's:
Photo RPM = 2880 x 720
Photo = 1440 x 720
Fine = 720 x 720
Normal = 720 x 360
Economy = 360 x 360
I could be wrong though, but there is definitely a progression.
Similarly, dot gain - a factor of the paper type - in more absorbent media, the dot spreads (dot gain), so less coverage may be needed, but the ink is laid down faster, and without using the smaller droplet sizes.
On low absorption glossy media, there is less spread, so ink is laid down slower, but maybe thicker, and smaller droplets.
If it performs like my C44, then setting "Text and Image", even for text only, gives a much nicer result - it sets the quality as FINE instead of NORMAL.
