Birchy, I use thease pullys on my mill conversion http://uk.rs-online.com/web/search/s...273+4294955369 RS usualy arent the cheepest but there service is second to none and delivery is free (usualy next day). I used a 10 tooth on the motor and a 44 tooth on the leade screw (used original leade screws as this was a tempray conversion just to help cut parts for my router build). Im only useing 205 oz in motors and get a max feed raite of 800mm/min so its pritty slow but gets the job done (can get 1200mm/min but sometimes loses steps at that speed). So i think useing your 425oz-in motors runing a 2:1 ratio you should get decent speed and still have enough power. Oh and as for concern about haveing enough "meat" on the hub of the small pulley for your motor i just put a grub screw in the center of the pulley bettween two of the teeth and aslong as you debur the hole propley you wont have any problems with it chewing up the belt. think i taped the motor pully for a M4 grub screw and the leadescrew pully M6. Btw my mill is a Champion mill from chester uk. If your motor shafts are 8mm Dia i would recomend atleast a 12 tooth pully.

I posted on this thread lastnight but it didnt show up, not sure what happend.

Hope this helps

regards
Simon