500mg, 750mg, 1000mg and above being moderately high. 1500mg is said to be optimal and from the effects I would say it is, but lower works fine too. I noted a rapid change even when I was on 400mg at the beginning so to whom it works, even small doses do the job. Higher dose appears to do the changes a bit quicker and more pronounced but anything above the optimal is likely a bit of a waste.
The blood pressure issue is interesting because I do have tendency for that, but for me its bad diet, smoking and alcohol that does it, all of which I have quit and cleaned up in last few years. Bad habits took blood pressure problems with them. NBE and HRT has done nothing negative to note about since I got DVT (blood clot) symtpoms from PM back before transition.