All the old measurements are related to the human body. Feet were... well... feet. Inches the distance between knuckles. I discovered the yard measurement myself, when I was trying to quickly estimate the yardage left on a bolt of fabric, holding the fabric from the tip of my nose to the end of my middle finger worked a treat. I've had this picture in my mind of short-armed fabric merchants in the markets of antiquity : ) Noah's Ark was measured in cubits. AndI guess in all these measurements, it was pretty handy being able to use something you couldn't loose.
Wealthy people were able to commission tools and weapons designed, weighted and balanced to fit the body measurements of the person using them. Perhaps you can see where I'm going here. I'm not sure that bigger is always better. At least not for hand guided machine quilting. I think it is possible for a sewing machine to be too big. There is a built in limit to how far we can comfortably push the sewing machine away from us and pull it back again. I'm hoping to find that window that gives us the space we need to execute our quilting designs yet stay comfortable. This is why I am so interested in getting feedback from people already using longer armed machines. Computer guided quilting is, of course, a completely different matter. Computers are not limited by human body ergonomics. But it is the human element in quilting which most interests me!
I'd like to thank everyone who has posted comments and emailed about the ideal length of your 'dream machine'. We are finding the responses really useful. Please keep them coming!