Also keep in mind that no WoW player notices a 0.01 difference in cast time for a single spell cast. The difference is only noticeable when you measure your DPS over a longer period of time. Each individual delay is not as important as you think.
That's the exact principal I'm going for, Individually each tick in WoW isn't very noticeable, but it does stack quickly. Player A can make off 10 attacks, while player B can cast 11 or 12 in the same time. In a long boss fight that can quickly add up to be dozens of more attacks player B managed than player A. Meaning a much better overall damage output.
All in all, what I've decided to do is use a tick_lag of 0.25. That'll give me that just-slightly-noticeable effect, and not completely destroy my server with a ridiculous processing speed. Thanks for all the help, I hope that 0.25 will be low enough for what i need, but high enough for the server to run without much problems.
You might want to wrap it in a datum so you can use the delays for spells and other actions instead of just movement.
Keep in mind that BYOND provides you with a general purpose game server. An mmorpg's server can be optimized to improve performance for precise spell delays and minimize network traffic. If you had mote control over the server's inner-workings then a tick lag of 0.01 would be manageable. Because of the way the server works, a very low tick lag is often detrimental.
Also keep in mind that no WoW player notices a 0.01 difference in cast time for a single spell cast. The difference is only noticeable when you measure your DPS over a longer period of time. Each individual delay is not as important as you think.