Jeff,
Shorter IS better, as long as you can reach your desired depth. Too many people buy , and use bits that are MUCH too long for their projects, and they then introduce deflection, vibration, and extra resistance by swinging the extra carbide around at 10,000+ rpm.
The "ideal" scenario is to use a bit that will get your cut accomplished without adding variables that will degrade the process. Some people buy a 2" bit "on sale"and then ONLY cut 3/4"material with it, and wonder why they have chatter, and machining marks...
A number of people are cutting their fret slots with the .023" bit, and they are getting great results.
"Share your knowledge. It is a way to achieve immortality"...The Dalai Lama
"Nothing is really work unless you would rather be doing something else....." Sir James Barrie