I just finished lvling my sage - Been playing Assassin before hand. I miss the options stealth give in terms of ninja'ing things, but outside that I find that sages are a fine class that can perform very well, and got a good arsenal of tools to work with.
Heres two vod's from some streams I did while gearing to partisan, so keep in mind that I am pretty undergeared, I am by no means the best or even close at playing sage, but hopefully it can help you with your decision on wether or not to try out sage for pvp.
Vod 1 - http://www.twitch.tv/upzie84/b/414641798
Vod 2 - http://www.twitch.tv/upzie84/b/412452901