Since not too long ago, it's best to set VSync to 'application controlled' and you can control this option in the startup video settings of the game. The same applies to AA (Anti-Aliasing).
As far as your connection, the speed isn't important, it's the latency and presence of dropped packets. You'll want to run a ping plotter for several minutes to the arenas' IP settings. These escape me right now but I'm sure someone will chime in.