The smaller the bits you use, the faster you need to spin them. So that's an argument for the Taig, or a Sherline with the high-speed pulley set, which can spin at 10,000 RPM. However, graphite is difficult stuff to work with. Even though it's sometimes used as a lubricant, when you cut it, it acts as an abrasive, which gets into the slides and screws and damages them. So you'd need to protect the moving parts of your machine better than they usually are, by providing bellows or a similar shielding apparatus. The other problem with it (besides the horrible mess it makes) is that the dust is electrically conductive, so if it gets into your computer, you can kiss it goodbye (carefully, in case it bursts into flames). I suppose there are ways of preventing this from happening - you might make another post asking if anyone has any suggestions on that.