Might just depend on your OS / Video Card. I run with vsync off on my PC (Win 8.1/GTX 970) and I get maybe 1 client crash a year on average. Do a verify on your GGPK to make sure no files are corrupted too, as corrupted GGPK files tend to cause stability issues in this game. Other that, I typically turn down all my graphic settings and disable chat, since those also affect the client.