I'm definitely gonna go with M&T's now.
Got ya. Ok. But if one of the rails has to move up a tad on one end to make up for any taper error, than the joint for that rail to post will not be 90 degrees. Correct?
This is all worst case scenario for me. I'm not sure if taper will be a problem at all. I didn't start thinking about this potential problem until recently (after starting).
Yep. I don't think I have a bow. All edges have been jointed.