In all fairness, ppl tend to mine underground so the surface is largely untouched. This world is also 15000x15000 which is a ton of free space. Maybe too much free space for a PvP server since ppl are too spread out.
yeah I think 2500x2500 may be a good idea too. theres no point in doing pvp if you rarely see anyone for days. I would actually suggest an alternative to the mining world. What about 2 or 3 times a week, the admins drop some 'ore meteors' onto the overworld for people to find and fight over. No claiming for area around the meteors since the admins can claim it an enable pvp around it.