Very happy with 8 here. We have big cables etc and 6 was fine...until winter. I put electronic ignition on the truck and it needs 5.2v minimum. My wife uses her truck daily and in the cold months the battery voltage during starting would drop below 5.2 and it was like having the key off.
Lightbulbs haven't burned out, headlights are brighter and the horn too. Regulator puts out 8.4 volts so I haven't even bent the arm to bump that up yet though I probably will.
