I remember that Bad Axe Games'
Trailblazer had a section talking about using the following progression for full attack actions:
- A BAB +5 or lower, you made a single attack at your full bonus.
- At BAB +6 through +10, you made two attacks, each with a -2 penalty.
- At BAB +11 through +15, you made two attacks, each with a -1 penalty.
- At BAB +16 and higher, you made two attacks at your full bonus.
As I recall, they showed the math on this, demonstrating that it resulted in characters hitting more often overall than if they got four attacks at the usual iterative penalties (the exceptions being where you were overwhelmingly likely to hit (e.g. only missed on a natural 1), or overwhelmingly likely to miss (e.g. only hit on a natural 20), since in both cases having more rolls mattered more than avoiding large penalties to those rolls).