So, if my FTP is 80-85% of what it was back at my peak, is that about all I can ask?
No, I would wonder why no heath professionals have warned you of ischemia resulting during hard exercise efforts. You may doing more harm than good.
My experience would suggest you should consider the risk/benefit ratio of any exercise levels. Like yourself, I have health issues that in theory should preclude exercising at high intensity - and like yourself I don't always ride with common sense as a guide.