I checked with support, and there is no way to make the spell check settings permanent. I have to set options each time. It's certainly not a selling point for AC, but in general I find the spell check helpful and generally quick to run through before saving a note.
My feeling is that the spell checker is as much a liability as a help, as far as time management. It does not come pre-loaded with medical terminology, which should be a prerequisite when part of an EMR. Plus, the inability to handle mixed case words, combined with the recent proliferation of med names such as predniSONE, is a significant flaw.