What hashrate does Bitcoin Unlimited need to have before this becomes urgent?
As long as the Unlimited hash rate is less than 50%, it is definitely NOT urgent. As currently designed, Unlimited isn't currently capable of forking with less than 50% of the global hash power.
If Unlimited has more than 50% of the hash power, you might want to start thinking about what you want to do. Financially it would be extremely risky for any miner or pool to attempt to mine larger blocks while Unlimited still has only 50% to 60% of the global hash power. They could try, but they would risk losing the entire block reward (that's a $12,000 gamble!).
As the Unlimited hash power gets higher than 60% the chances that some miner might try mining a larger block increases. If the Unlimited hash power exceeds 75% you should probably consider it urgent if you haven't done anything yet. It's entirely possible that no miner will risk it until there is over 80% or 90%, but there is a chance that a miner might give it a try below that.
