Setting up Gecko 210 - Step settings?

Hi,
I need some help about the settings for a Gecko 210 (in regard to
the stepping settings).

I'm using them to drive Vectra stepper motors on a Sherline mill.
The motors are 2 Amp, 0.9 deg/step.

Should I set the Geckos to single step, half step, 5 or 10
micro-step on the jumper blocks?

I am assuming that the half step and micro step are slower since
there are more impulses per motor step, or can this be offset in the
software? With the motor doing 0.9 deg/ step is there any practical
advantage to using half or micro-steps?

Also, I've set them up to use a +5V common (the breakout board is
set likewise). I haven't really found any info explaining the
advantages vs. disadvantages of using a +5V vs using the ground as
the common. My breakout board can be set to either setting as well.
Any thoughts on this?

Thanks in advance...

FWIW, I am building the controller following the series found in
Home Shop Machinist and written by Roland Friestad. His plans are
very robust and expandable - he's left room for almost every option
you could imagine. Everything including the computer fit on a single
aluminum plate that fits inside an industrial enclosure. It's a
pretty slick set up for someone building from scratch that wants a
compact and efficient set up. After getting some experience with it,
I plan to use it on a full size mill.

Regards,
Joe Travis