I think 2 servers with 2 different pvp setups will not work. One will stay heavily populated.
Aside from possible issues, 2 severs might be a good idea... interaction probably won't be too heavy starting out anyway, it will solve some of the territory issues, maybe, and i assume it will deal with the whole terraforming/lag issue that seems to have cropped up with so many people doing it at the same time.
Then again, an empty world would be boring as tribes become more advanced... but by then hopefully the issues would be fixed by then and the game could handle more players.
At a guess i would say... 2 servers earlier release, 1 server more problems, later release. Just a guess though