Without a doubt I would go for the non-intervention test with a CT angiogram and calcium score including pulmonary system, heart and descending aorta. You are a good candidate because you have a family history and you don't have CAD confirmed other than an EKG showing depressed ST segment. Your exercise tolerance is very good, but you have chest pain that comes and goes for the last 2-3 years and the pain didn't occur with the completion of the test.
The CT scan with calcium score will show whether you have any early signs of CAD as well as any hard plaque buildup within the lumen of the arteries that may be causing chest pain. The images of the lungs and pulmonary artery will rule out any blockage and/or blood clots that could cause chest pain.
There is no urgency for a test, but having a family history you will want to establish a base line for future tests going forward if and when it becomes a medical matter of concern. You should maintain a healthy diet, exercise, maintain proper weight, etc.
Thanks for sharing and if you, and if you have any further questions or comments you are welcome to respond. Take care,
Ken