[mkr-hn]

New users could start with a 24 hour limit between submissions (86,400 seconds) and get 20 seconds removed for every karma point. Someone with 2000 karma would be able to submit every 12.8 hours. By 4000 you've probably learned that quality beats quantity.

[mnutt]

That seems fair, though it might be better to use average story karma. The bots in question probably have a fair amount of karma just from the sheer number of stories submitted.

[mkr-hn]

Multiply the value by their average. It boosts overall submission quality automatically by giving better commenters more chances for a front page article.

edit: Though the value would need to be much lower than 20 per karma with that modifier. My average of 2.73 with 2011 karma would let me post as much as I want.

karma * 3.7 * average would come to around 20,000 for me. That would let me submit an article every 18 hours.