It depends on quality options selected. Below is for P800 (from RedRiver site)
Quality Options
2880 x 1440 dpi (Level 5)
1440 x 720 dpi (Level 4) - Lowest choice available for glossy, luster, fine art settings
720 x 720 dpi (Level 3) - Available for photo matte and plain paper media settings
720 x 360 dpi (Level 2) - Available for plain paper media setting
Interpolation in the computer will, almost always, be better than in the driver/printer. Plus, one should assume that, in the computer, sharpening will be adjusted for the dpi (really ppi). Qimage does this for you automatically.