We are the same age and on somewhat on the same marathon. My score on an initial calcium scan was 398 about 8 years ago. It wasn’t until I connected with my current cardiologist (and care team) that my true risk factors have been identified, and then improved. Instead of a ‘spray and pray’ approach they are figuring out how my specific body works. I can tell you my body like this approach much better.

You mention you do not have symptoms. Why did your primary doc recommend getting a calcium scan? What is your cardiologist looking at to think you should cut your exercise? I guess my suggestion would be to ask questions before changing any habits. I listened to doctors who told me diet and exercise don’t matter in my situation, turning out to be bad information.

It may help you to ask, given this new information what your LDL target should be. Questions are good and your blood can answer a lot of them. I am certainly not an expert but I can provide a few places to get your started (Maybe these are already posted in the thread-sorry if repeating):
There are blood tests that break down your lipid numbers even more. One example is Apo B that is part of your lipid panel LDL number. https://my.clevelandclinic.org/health/diagnostics/24992-apolipoprotein-b-test
There are additional genetic factors that can be easily checked https://www.heart.org/en/health-topics/cholesterol/genetic-conditions/lipoprotein-a
My doctor periodically checks my ceramide score, an independent risk factor for inflammation. What goes into the score seems complicated to us but it does give our doctors more information to work from. https://www.mayoclinic.org/diseases-conditions/heart-disease/in-depth/heart-disease/art-20049357