I couldn't tell you what's bad for boxing as I've never done it on anything but broadband. My highest pings were on cable where they were about 110 on sundays and 60ish on off-peak times when I was in Houston connecting to one of the Dallas PVE servers. Magtheridon is in Dallas and I'm up here too now, which explains my completely OP pings. My FiOS stuff now is usually between 8 and 20ms. :P I would think, though, that server lag would be worse than your latency. You might suffer issues when doing epic mounts or shattrath but everything else should be OK even with pings up to 500.