Robert,
Feed rate for an end mill or slot drill is not a science but a compromise, dependant on machine rigidity, main drive horsepower and axis drive power. The best guide is to set the machine up and manually feed the axis, you will feel and hear when you are going too fast or too slow. Chip load per tooth, as quoted by the cutter manufactures, is only an initial starting guide. In most cases if you can achieve it on a hobby type machine, you are doing well. Experience and confidence in your machine lets you get closer to what your particular machine can do.
Graham has pointed you in the right direction and I have attached here a .jpg of a chart I made years ago which I have pinned on the wall. This gives me a guide to get me in the right ballpark.
Ian