You'll never get that motor to spin very fast on 24V.
Typically, the larger the motor, the slower it's max usable rpm.
Geckodrive has a formula for power supply sizing, for maximum motor performance. 32 x square root of the motor's inductance.
For your motor's, to get maximum performance, you'd need to supply them with about 150V, about 6 times what you have. Since usable rpm is proportional to voltage, you're basically only getting 1/6 the maximum rpm that that motor is capable of.
You might want to try a 72V power supply, which should be 3 times faster. Better still might be to gear up, so that the motor spins slower while moving the machine faster.