Doug,
My shopbot is an older model, (2003 I believe) with the 4G upgrade (2007?) its a standard machine, not an alpha... I'm not sure what machine you are using, but for me, I'll let the machine take its time, I had my time into the original sculpture, and can work on other things while the machine whittles away on the foam.
It is an 8" block, and I want to say this file took about 6-8 hours to cut. I wish I could afford a faster machine, I'd be doing much bigger projects that would really blow your mind. I just don't have the ability to babysit my shopbot 24 hours a day. Someday maybe.