KY, I think you could go more than 4 + 2, if you wanted. The angled ones can be very close to the outside verticals, b/c the reels never get close to each other. In my pic in post #5, I have 5 vertical, with the two clamp ons, and the factory spacing could have easily been closer. I did the same as you for the angled clamp on, except I attached it to the inner brace, to get the rod holder out of the head space in the walk around.
I would go lower than 45* an the angles, like 15-20. If you are trolling from there, it is hard to get the rod out with a keeper on.
On the bigger boats, do any of the rocket launchers get supported by the top frame? Mine is just bolted through the fiberglass behind the cross member tube, and it has more flex than I like to see, in that 8" or so, of overhang.