Just thought I would put this here: Today I fixed a quarry that was approximately 96x96 blocks. I feel like that's completely unnecessary. Please keep your quarries at common-sense dimensions to make gameplay fun and lag free for everyone. Also, running water blocks cause lag, and if you aren't careful, you could easily cause SEVERAL chunks around you lag out. Same as with quarries, please use your common sense. If you have any other known or suspected lag-inducing machines or items, please post it here so it can be confirmed or denied. AKA...this thread is the Mythbusters of Feed The Vault
The only reason to be running a quarry larger than something like 25x25 is if you're excavating your basement in your 50x50. And even that can be done in sections. :/