I don't really know if is my PC problem or not, but i saw few people with this issue around.
When i start playing any server, most likely new ones, the frames per second go fine.. but then i teleport or i start killing, and the game go very very slow, like a very old PC running RO with 64m of ram lol..
And then i checked the Game Process.. and it was in Low Priority.. and when i change it to normal or any other setting, it change again and again to low... weird.
I have some normal 2gb of ram || Dual Core.. is not really a system requirement issue, i always played RO without problem.
I also tried to fully reinstall RO, but no results.