My Way too complicated and 'application specific' to discuss beyond generalities.

As the motor gets larger relative to the original port cross section (think Stroker) it's much more of a challenge to get enough air IN to the motor and if you can't get enough in there's less proportionally you have to worry about getting OUT. If VE is falling by default so are the pumping forces. The tuning objective for just about any motor is get to optimum VE as early as practical for the application/load/gearing and keep it there (as close to peak) for as long as possible/practical.

The intake closing event effects overall torque and power curves more than any other single event....for a given application you more or less select the cam for the type of engine tuning (powerband) you're looking for, the exhaust timing and lobe spreads are selected from there.

Also remeber it's harder to fill the cylinder than to empty it...you have to induce the air/fuel into the hole past the valve typically with little or nothing more than Atmospheric pressure....but once it's detonated those expanding gases are LOOKING for somewhere to go....where would they go if your exhaust valve didn't open? They'ed go out somewhere, woudn't they???? The exhaust pattern/duration is a tuning means aimed at tuning the pressure (as much as possible) and to ensure adequate evacuation without upsetting the next intake charge. Backpressure through the system (as the high pressure gases return back to atmosphereic) acts like a resistive force that somewhat slows the rate of acceleration of the crank, which in turn generates the draw on the intake charge....but that resistence is also summed along with all the other resistive forces acting on the crank....namely the recipricating/rotating masses as well as the drag from the rings, bearing and valvetrain.

Also as Jim correctly illustrates the @.050 duration only tells part of the story, many cam grinders use a "lazier" exhaust pattern in an effort to trap cylinder pressure a bit longer where as with the intake you want to snap it open to get to full lift sooner and then snap it back shut before the piston sweeping back up past BDC bleeds combustion pressure back into the intake tract.

I,ve always loved Polysheric's posts but I wish he'd get a little thicker skinned; it's a forum afterall and if I ran off every time somebody disagreed with me (even if they were wrong ), I'd have been gone a long long time ago. Or maybe in myu case I'm just too hard-headed to take a hint that nobody wants me around!!