You don't indicate what type of work you will be doing, and what size tooling you'll be using most. RPM is determined by tool material, tool diameter, and work material. If you'll be using 1/2" HSS tools in aluminum, you *want* to be turning about 3100 RPM, and feeding at 10-15 IPM, faster for shallow cuts. If you'll be using 1/8" HSS tools in aluminum, you *want* to be turning about 12,000 RPM, with about the same feed rates (maybe a bit less).
So, yes, 1750 RPM will SERIOUSLY increase your machining times. Except for larger tools, you don't need more power, you need more RPM. you can probably get away with perhaps doubling the RPM by changing motors (get a 3-phase motor and VFD, which will allow you to double the motors base speed, and give you variable speed), or gearing (a LOT more work). Better still, get a mill that already has higher speed capability. Syil has an X4 mill with, IIRC, a 24K RPM spindle. But, it may be vaporware.
I can't for the life of me understand why all these small mills have such low speed spindles, as it is a serious performance limiter. Of course, given their limited rigidity, you aren't likely to reach the above rates on other than very shallow cuts anyway. $3500 just doesn't buy you a very heavy duty CNC machine.....