The finish temp is whatever you want from 160ish to 200ish depending on your desired texture.
I think you will need 180 (+) and some time in steam or foil to get "tender".
Slicing across the grain helps also.
One thing I have heard and read, is that no matter where ya take it to temp wise, cool it all the way, fridge it over night, you can get it to slice much thinner, and for pastrami, the thinner the better for me at least, more surface area for flavors to do their thing. I like mine arby's thin, (usually requires electric slicer)