My ideal sewing cabinet would be about 3-4 inches lower than table height. How tall or more precisely, how long torso you are will determine your ideal height. Adjust your sewing chair so that when sitting, your knees are at a 90 degree angle. Sit up straight and put your elbows at a 90 degree angle to your forearms. How far your elbows are from the floor should give you the correct height. Most people lean forward a bit while sewing so the comfortable height may be a couple inches lower. Other people put rubber door stoppers under their machine to tilt it towards them slightly to correct that posture. Whatever is most comfortable for you would be the correct answer. I don't like the rubber door stopper trick because then I bend my wrists.