Update
I decided to take the plunge and go for the 1.5HP Leeson motor. Unfortunately, when I called the supplier, they said the motor was out of stock. I called multiple suppliers (whose websites claimed it was in stock) and they all said that they won't have any for two months. As far as CNC conversion projects go, 2 months isn't that long, but I was disappointed as I really felt like I was starting to get some good momentum with this project.
So, in the meantime, I realized that their might be a simpler method for increasing RPM without even having to do any machining. Why not just replace the DC drive for the PM-25MV with something that could drive the stock motor at a higher RPM? After doing some research I bought a KBCC-125R DC Motor Driver. I found a good deal for a used one on ebay. The KBCC-125R model includes a breaking resistor and reverse capability. If I understand the driver correctly, I should be able to get up to 5000 RPM. Not sure what will happen if I double the speed of the stock motor. I guess we'll find out if I can get the DC drive to work correctly.