Stepper motor size question.

Hello Everyone.
can someone help please? I have bought the flashcut 3.5amp
microstepping drive and software. I would like to put larger motors
onto my mill but am not sure how large I can go. I would like to buy
the Motors in the uk as I live there so this would cut out the
postage and import costs. I have seen some size 34 motors at Alzanti
http://www.alzanti.com but all the size 34motors on the stock list
are rated 4a/ph.
can anyone share their experience please, does anyone run the
flashcut 3.5 amp microstepping drive, If so,would you mind telling me
which motors are the best to use.
Thanks in advance.
Graham.