Maybe I wasn't clear enough above.

The motors are 4.5v, 2.5A per phase to be wired bipolar.

I was originally thinking of wiring them as serial to match the 2.5A controllers, but after reading the other thread it mentioned that you get greater torque if they are wired in parallel - that would, I presume, double the current being drawn from the controller - thus needing a resistor to limit the current (ohms law).

The motors are from Arc Euro Trade - 180Ncm (can be used bipolar or unipolar)
The controllers are the Routout 2.5A ones

The power supply that I currently have to hand is 12-14V (varies a tad under load) @ 10A.

I will get a better PSU at a later date, probably around the 25v mark.