PJ80A2-20

I've found spec sheets for Inland/Nippon PJ80A1-20 and PJ80A2-24, but
I have some PJ80A-20's and it is not clear to me what the
difference(s) might be. The motors I have are 6 wire, and marked 200
steps/rev and 1.68 ohms per phase. The A1's show the same resistance
and 3.36 volts (so 2 amps) per phase - would that then seem to be a
good place to start?

I have one of Dan Mauch's bipolar chopper boards from early 2000's,
might I use a higher voltage, or stay with this seemingly low voltage??

Thanks, Chuck