You'll get higher low speed torque from a DC motor of a given power but for a given spend on motor and controller you can get a much wider speed range from a 3 phase motor & VFD.

I run a 1hp 3ph 2 pole motor at 7000rpm all day on my benchtop CNC Mill, the VFD is Siemens, the motor is a Compact Frame Electro Adda. My Myford S7 has a 1hp 3ph 4 pole TEE motor and a Siemens VFD, the motor and lathe are comfortable at 3000rpm.

For a given total spend you will probably be able to get a better spread of power, torque and speed using a 3 phase motor with the right power and gear/pulley drive ratio but that will probably cost more than just replacing your DC drive.

- Nick