different drain resistor values on a MOSFET

[mordechai]

In looking at some of the ZVex circuit susing MOSFETs (e.g., Box of Rock, SHO, etc.) and other circuits like Jake Nagy's Blue Magic or ROG's Peppermill, I see some differences in the drain resistors on the MOSFETs.  Vex seems to favor a 5.1K resistor (so, a 1.2K+3.9K) while the Blue Magic and Peppermill use a 4.7K resistor in that spot.  Other MOSFET circuits like the Catalinbread RAH and WIIO use an even lower value (3.3K, I think).

How do the different values affect the way these MOSFETs function?  Does a higher or lower value lead to harder clipping or more gain? 

And what would be the effect of having different drain resistor values for different MOSFETs in the same circuit (e.g., if Q1-Q3 of the Box of Rock have drain resistors of 5.1K for Q1 and Q2 but a 4.7K for Q3)?  Would this have an adverse effect on smooth cascading of gain from one stage to the next?