A500 or A518 ??

Is the extra weight and extra strength of the A518RH really needed for a daily driver with less that 350 HP ? or will the A500RH be a better choice. ?
The only reason I ask, is because , I'm not having much luck finding an A500 RH locally. I'm not in any great hurry...but still I can find A518RH's much easier.
I would prefer the lower gears of the A500RH, and less parasetic power loss.