Don't go up to 45V. According to the datasheet 50V is the absolute maximum rating, so you can never go over that, which makes only 5V lower almost certainly too close with an inductive load. The datasheet reccomends up to 42V. It accepts up to 4.5A, which is good for the 3Nm stepper motors in bipolar-parallel, since they're 4.2A.

Datasheet:
http://www.kosmodrom.com.ua/pdf/TB6600HG.pdf
Cheaper versions:
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It looks quite promising, but I doubt I'll be getting many as for the 3Nm motors it's better to run them from 75V.