What are you using to create the code.
Most drawing package do not produce arcs and circles, but produce straight lines, to the eye they look smooth, but to Mach they look what they are - a lot of straight lines. You description of getting choppier towards 45 degrees reminds me of the effect I get drawing a diagonal line with too much magnification
Look at your code and see if this is the case. If pockets you are cutting are circular, this shold be a G2 or G3 move, in which case I would expect you to get a perfect circle. If the pocket is square or whatever, is there any way you can increase the resolution on your drawing package. My Turbo cad also has a setting for the number of sectors in a circle, which can vary from eight or so, up to whatever - I usuall use 360.