I think it's really important to experiment with the heights you use. I hunch if I use a machine that's shorter (like a featherweight) even if my elbows are at 90 degrees. I cut way higher than most people say you should, but I can go at least a half day without pain, even with 2 bulged disks in my back. Use 2x4s to raise tables and such to see if you want it higher and give it a good test, not 5 mins and decide no. To "lower" for testing, I leave my table at its default height and raise my chair and put my pedal on a raised block or something. I wrote about some of the ergonomics here:
http://www.archaicarcane.com/high-en...r-sewing-room/ - There's cutting table stuff below the LA stuff. One thing I said in the post and something I will always stand by is "Your tools must conform to your needs, not the other way around."