The 3Nm stepper motors are used on most builds as they are good value for money, so that's a good buy. Did you get 3 or 4 motors? For the size of machine you're planning on 4 would be best so you can have two ballscrews on the axis that moves the gantry, or you can link the axes with a long timing belt so that only one motor is required.

The torque from a stepper motor is proportional to the phase current. Therefore the torque reduces as the motor speed increases since the inductance of the coils limits how high the current can reach before the next step. To combat this you need to run the motors on a higher voltage, since this increases the rate of change of current. The motors you have chosen can be run on up to about 75V, so it's best to choose drivers rated for at least that. Currently there's plenty of 80V drivers available on eBay, such as these:
Cnc 7.8A,80V,256 Mirco digital Nema34 step motor driver | eBay
CNC Micro-Stepping Stepper Motor Driver 2M982 24~80V 7.8A Controller | eBay

I bought quite a few of the DQ860MA and found them to be a little better than the m752's I have.

Next question will probably be what power supply do you need? Getting a toroidal transformer and making it yourself is the best option and there's a few discussions in other threads about how to do this and why. Or I can show you...