Charlie,
We just converted from DOS in the past year and went to 800 x 600 from the start. We were lucky because we download from an auto body estimating program that is used by about 13,500 body shops and they went with that size. So if they run that program they can run ours. I always try to think "what do I whish I had done one or two years ago" while imagining myself one or two years ahead of today. It takes so long to write good software that I try to design it for the hardware that will be the entry level stuff by the time I have it ready for use.