Either way you end up with a 48v battery bank that has a certain amount of lead and therefore amp-hour capacity. With an 8v (GC8 size), you get a physically larger battery and the higher voltage yields more watts of power, but fewer of them fit in the cart. From the performance perspective, you need to think in terms of

__a single 48v batter__y of some amp & wattage capacity. If 6 x 8v ends up with the same total amount of lead as 8 x 6v, then you have identical battery banks and the performance will be identical. The difference (if any) will be upfront cost.

You can easily get bogged down comparing amp-hours, cycle life, recharge frequency, upfront cost, etc. I'm not sure if any of that makes much difference in practical application. Maybe

this article will help, but be aware it may be biased towards the 6v batteries advertised therein.