BTW I just noticed that you have things like pixel accuracy set quite loose - If your shaders are grainy (quite clumpy patterns) and the pixel accuracy setting is low (as in fast 'n' dirty), the render quality won't be very nice because it will just skim over dark/light patches without nicely rendering the inbetween colours and tones. If you set the pixel accuracy to a smaller number, the render will achieve a better subtlety.