Take a piston with a 5.7 rod and put it in an engine, put a dial indicator on the piston n turn the crank with a degree wheel mounted on the crank read the dial indicator as the piston moves from .001 btdc to .001 atdc, the degree wheel and crank will move through about 3 or 4 degrees of rotation.Then do the identical experiment with a 6 inch rod and the appropiate piston,the degree wheel will move 9 to 10 degrees over the same range of piston movement,this is important during the transition from the compression stroke to the power stroke, by increasing the piston dwell you allow the pressure to build higher while the minimun cavity exists in the chamber, this higher pressure level translates into more effort on the piston during the early potion of the power stroke.
Crank arm also swings further before the combustion cavity begins to open, this allows the pressure of combustion to be more effectively transmitted to the crank arm while the pressure is the highest.
If I could put a foot long rod in an engine I would do it!
Of course this cant be done in a sbc or any other gas eng. that i know of.
And there is my 2 cents worth on long rods.It works,just make sure you initiate ign properly and tune cam,intake,and exhaust for this.
RPM doesnt matter.Always worked for me!!