You're right, I splashed the cash and bought.
Mach3 CNC controller
[snip the math and analysis]
The resolution of the machine is irrelevant, it's the tool size that matters. If you have a 1/2" diameter end mill, you cut a 1/2" swath through the material. It makes no difference if you have 0.01 inch resolution or 0.00001 inch resolution, you'll still step over by about 1/2 inch when using that tool.
So you can see how optimised tool paths, and so on are literally god when it comes to CNC.
Yep, for production machining, optimized toolpaths are a very good thing. The common limiting factor for small machines though is spindle horsepower. The machine can only remove so much metal per hour, and that's directly proportional to the spindle horsepower. It varies with many factors (cutter material, cutter coating, cutter speed, coolant/lubricant, etc), but it's the thing that limits the depth of cut you can use for a given end mill. There's also no such thing as an "optimal path". There are many factors that determine what may be optimal in a given situation - surface finish (the look of it), surface roughness, tool life, machine rigidity, and more.
Sure, there are free OS alternatives to the stuff I paid for, but I don't have the time left to live, nor the inclination to pay the electric bill, that using the free OS alternatives requires.
I sure hope you're talking about non-optimal free CAM, because as it happens, the most capable machine controller available (for less than $5000) happens to be the open source one. I only put in the price limit because I hope that the vendors selling the more expensive controllers actually have some better features than EMC2 - I know what you have doesn't.