Hi Sue,
OK I am totally biased for the Innova we will get that out of the way right now. Harp space makes no difference in doing a king, it is the rack length that matters. A 10 foot rack really only gives you about 100" of quilting width. Even then it a tight fit. So for a king you will want at least a 12 foot rack better even a 14'.
A good rack makes a HUGE difference and all bias aside the Innova rack is an engineering marvel.
1. It can be adjusted for many user heights so if you are vertically challenged it can be set up to YOU.
2. the dead bar is wonderful in that you don't ever have to make adjustments to your take up bar as your completed quilt grows. Many other makes you must make adjustments to the take up bar. Additionally because the take up bar on the Innova is high up off the machine bed you lose very little quilting space
3. It is made of aircraft grade alluminum. Very sturdy, won't bow in the middle as it is all one piece and minimal vibration.
4. NO Learning curve with the Innova rack.
And the lightening stitch is a thing of beauty. It really is the most responsive SR on the market today. But I understand A1 is coming out with something just as good right now.
between 18" and 22", consider a 12" block on point. You will not be able see the full block in your quilting space with 18". 22" you will.
Edited to add Innova customer service IS indeed 24-7 INCLUDING holidays. I had a problem over the Christmas long weekend and 3 techs called me back within 20 minutes, INCLUDING Michael, the owner. He walked me through a workaround that got me back up and quilting. THAT is customer service.