Bill, as for opinion, I totally agree with the approach to preemptively take care of the dilating aorta.
As far as a "less intensive coag" requirement for home testing (such as a lower INR), I can't imagine where he got that notion. As far as anything I've seen anywhere, "T'ain't so, McGee." INR is INR. It's better to do at home, but you're doing the same ACT.
There is genuine data for Carpentier-Edwards bovine valves and St. Jude porcine/bovine valves exceeding 22 years on average in older recipients. The reason there isn't data for 25 years is due to the fact that they haven't been around for 25 years yet. Over the last few years, it is becoming more common for people of your age to obtain biological valves, rather than mechanical valves. I'm 57, and just had a St. Jude Biocor tissue valve implanted three weeks ago.
Many doctors get much of their valve information from the salespeople they see. That is usually noticeable because of certain, fairly common, inaccurate notions that seem to pop up, that would seem to emanate from a common source.
However, there's nothing wrong with a mechanical valve, either (particularly the On-X). That also doesn't mean anything about how good a surgeon he is. He sounds like someone you can trust your chest with.
We're the worst people to ask about our own symptoms. People tend to either ignore/deny them or to frighten themselves into believing they have every one. It's likely that you do have symptoms, but have successfully adjusted to them. For example, angina often shows up not as pain, but a slight tightness at the top or base of the throat (in women especially, it can be jaw pain that actually sends them to the dentist). Nor does it always follow exercise. Some people ignore palpitations, or just think their heart is beating a little hard from some activity. The symptoms of AR and AS build up very slowly over time, and we usually assume they're just the slow result of wear, tear, age, and activity. Day by day, there's nothing to see. What may well happen is that a few months after the surgery, you'll suddenly realize how much the stenosis had really been holding you back.
At .7cm², you are well into the surgery window, so it's good that you're scheduled. I wish you good fortune with the path you have selected.
Best wishes,