Finer step angle

Hello,

I was looking for a NEMA17 stepper motor for the second extruder I am making. I stumbled on to this web site, which sells a few variety of stepper motors. The price looks decent, too.

However, the motor I would like to get has step angle of 0.9 degree, which is half of the step angle of all the other motors I have on my printer.

If I want to use this smaller step size motor in my printer...

1. I have to make updates to the firmware, and my RAMPS will be able to control this motor more accurately.
2. I don't have to make updates to the firmware, but it will be a good idea to do so b/c my RAMPS will be able to control this motor more accurately.
3. I don't have to make updates to the firmware, this motor will be automatically more precise thanks to its smaller step size
4. I have to make updates to the firmware, but there will be no gain in accuracy
5. I simply cannot use this motor.

Which one of above will be correct?