DC motors to servo's (was Gecko burned)

Info snipped from Les' post - my question at the end

>Hi Keith,
>
>I will be using treadmill motors from surpluscenter.com, item number
>10-1573. Carriage to the UK cost more than the motors but they are
>still
>lots cheaper than anything I can get in this country. Surplus center
>were very helpful.
>
>The motors are designed to be foot mounted but they have a nice big
>flange on them that can be drilled with the same bolt holes as the
>current motors. They are smooth to turn by hand with only a little
>'cogging' and will run down to about 1.5V.
>
>I intend to use 200CPR encoders(giving 800 steps/rev) and I will
>probably gear them down 4:1, giving a resolution of 16000
>steps/inch.
>The Z axis will probably stay 1:1 because I don't fancy trying to
>change
>the belt :-)
>
>I will go with Rutex drives, not because I have anything against the
>Gecko drives but because I have future plans that will make use of
>the
>SPI facility.
>
>I will let you know how I get on...
>
>Les

I'm just wondering how accurate a servo can be made using this
method? Will you be able to get similar repeatability and accuracy
with this type of servo?

Thanks

Rod