Though I guess this is wandering into house rules, what do you think would be a balanced feat as far as giving up iterative attacks for a better crititcal chance? Would a 1 or 1 be fair? Looking at the numbers, I think maybe losing one iterative for a two increase in the threat range would be more fair.
At 15th level, my archer can attack with rapid shot like this:
+34 +34 +29 +24 for d8+15 damage & crit 19-20x4
Using this proposed feat, this would become one shot:
+36 for d8+15 damage & crit 15-20x4
And next level, it would turn this:
+35 +35 +30 +25 +20 for d8+15 & crit 19-20x4
into
+37 for d8+15 & crit 13-20x4