Rods, the long and short of it.
The decrease in side loading while an improvement in power and durability is only a minor part of the equation. Increasing the length of the connecting rod will improve the pumping characteristics of any engine and increase its combustion efficiency by extracting more power out of the same amount of fuel and air. The physics of this gets a little complicated, but much of it has to do with the position of the piston relative to the combustion chamber as the crankshaft rotates.
The longer the connecting rod, the longer it takes the piston to reverse directions at either end of its travels. The rod has a wider swing than with a shorter rod so during combustion the piston is higher with more pressure against it when the crank and rod are at a 90* angle to each other when power transfer is most efficient. This extended transition time translates into a greater latitude in ignition timing. You can reduce the timing advance and still be able to achieve complete burn because the piston is traveling slower at the top of the cylinder with the longer rod. Reduced timing generates less negative pressure against the piston before the crank has swung past TDC and started back down. Because of this improvement in piston speed geometry the charge generates it's maximum combustion pressure while the piston is higher, therefore applying it for a longer length of the stroke and generating more power from the same amount of air and fuel.
When combustion efficiency is improved, sensitivity to detonation is also reduced. The advantages above also allow a higher static compression ratio, in fact if you lengthen the rods enough you can increase compression ratio and reduce octane requirements at the same time. This will again increase engine efficiency and reduce timing advance needs allowing each to maximize the other.
At the other end of the stroke, BTC, the slower turn around happens again with more good effects. The piston hangs at the bottom of the cylinder for a longer time, allowing for a more complete cylinder filling on the intake stroke, and on the exhaust stroke it allows for more reduction in cylinder pressure before the piston starts back up which reduces pumping losses.
The more efficient piston movement due to longer rods will improve the flow of gases into and out of the cylinder and will dampen a cam with large amounts of overlap and duration as valve timing events are still happening at crank speed, not piston speed. This makes the engine less sensitive to valve timing and intake and exhaust systems. On the exhaust to intake stroke transition the slower piston forces more exhaust out and allows the exhaust valve to shut and the intake valve to be further open and more clear of shrouding before the piston picks up speed and pulls away. This reduces exhaust gas contamination of the intake charge greatly, especially with high amounts of overlap and exhaust system pressure. The increased piston speed at mid stroke coincides with the intake valve achieving it's maximum lift thereby generating a harder pull on the intake and better cylinder filling with less power used to do so. At the bottom of the stroke the piston slow down allows the intake valve to shut further before the piston reverses direction again, this traps more charge in the cylinder with less intake charge reversion.
Because longer connecting rods get more power out of the same displacement they increase overall efficiency by about 5 to 10 percent at the ground. They will generate more horsepower and torque than the same engine with shorter rods and produce a wider, less peaky, power band. This is how they work and why spare no expense professional racing motors will have the longest rod that can be fitted into its dimensions.
Is it worth it for you and me? I would say yes if you can swing it, but to achieve the greatest gain you need to know what it is you are doing and why, that way you can tune for them accordingly. The specifications that generated maximum power with your shorter rod combination will not carry over. You can and should run more cam and compression and less ignition timing.
Is that detailed enough for you?
Vernon