I know about the heel on pedal rule for seat height, but my calves and achilles tendon have been aching after every ride since I raised the seat to get the maximum slight knee bend. I tried lowering the seat a little bit today and rode and I had NO calf or achilles soreness. Is this OK for the knees though?
What maximum degree of knee bend is safe on the knees when lowering the saddle?
A lot of the published "rules" for seat height are directed at young riders who are racing. Most regular riders may find it more comfortable to ride with the saddle a half inch, or even an inch lower than a "racing" position. People who ride on rough urban steets can benefit from the ability to ease up off the saddle a bit when the leg is fully extended. That means that when the pedal is at the lowest point, you can see some bend at the knee.
A bit of "trial and error" is helpful, but try to stay with one position for at least a week so that you and your legs get used to it before trying something else.
Now that I think I have a height that works well for my age, condition, and riding needs, I have set all of my saddles to an identical height. If one of my bike saddles were an inch higher or lower, it would not feel right at all.