One of the things you’re not telling us is the RPM you are running, is your RPM controllable or are you stuck with a set RPM? You need to understand "chip load" (Google “chip load”). If you increase your feed-rate you need to increase the RPM of the tool in order to maintain the correct chip load, increasing tool diameter does not help and might hurt. Besides understanding chip load you need to look at the surface speed of the tool, increasing the diameter of the tool will increase the surface speed of the tool and might not be helping. In short the spindle speed of your machine and the tool in use along with the feed-rate will determine the chip load. If you want to increase feed rate you need to increase RPM.
Greg Rockwood
Machine tool repair and rebuilding in Los Angeles CA www.Studwellengineering.com