I'll probably keep the regular 8K/rpm spindle but add the TSC as its not even 4K for the option, 285psi pump/filters and all included, seems really good. I'm just thinking that its rare I'd need 12,000 rpm, but the 8K might have a little more torque at low speed "if" its belt driven, and hopefully cost less to rebuild if/when needed.
You site the difference in cutting feed as an influence in your decision making process, but don't see yourself ever needing 12K RPM? This would be your first CNC machine, based on your other posts I'm not sure that you have previous CNC experience? Do you have a CAM system that would make the processing speed of your control relavent? Do you have prior CAM experience? If the answers to these questions are no I would suggest buying a used CNC (early 90's or newer) and a CAM package. You can get a perfectly servicable used CNC for 10-20K and you can use this machine to absorb the inevitable learning curve (oh shits) that will be associated with learning a CNC machine and a CAM system especially. There is no sense in having a fast sports car for driving a winding mountain road (CNC machine with no CAM system) And it makes even less sense to learn to drive using a new sports car.