Are you saying running 2 hrs at 50% is better than 1 hr at 100%? Does it matter how your SWG accomplishes the % output? Some just turn on and off to get the desired %. But I think my CompuPool actually adjusts the voltage to the plates.
Cell life is usually measured in Amp/hours, so 2 hours at 50% is EXACTLY the same as 1 hour at 100%. To get 50 % power, the controls shut off power to the cell, either abruptly (relay) or tapering (solid state relay.) That opens the great debate about what is more damaging to the cell, steady-state operation, or cycling. Cycling the polarity reversal (cleaning) is known to shorten cell life, so you definitely want that to occur as little as needed to keep it clean, so why power cycle it at more?
The pump is using much more power then the ECG. I would determine what pump run time is required to filter the pool, and adjust the % to fit that time period. If you get too little FC at 100% in that time, then you will need to increase the pump time. Too much, then decrease the %.
The things really don't make that much chlorine at full power, so if you want to maximize cell life, why not run it there when you run it? Put it on its own timer and set it at 100% power so that it is not cycling power, and possibly reducing cell life.
The general advice is to run your filter pump sufficient number of hours to filter the pool and mix your pool chemicals. For most people this is 8 hours or more. Set the SWG per cent to maintain a least a 4 ppm FC. The filter pump requires substantial amount of electricity; the SWG requires very little electricity to operate. You will minimize your use of energy by running your filter pump the minimum number of hours required to filter your water and adjusting your SWG accordingly.