DDOS Deflate Safe Connection Limit?

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http://serverfault.com – I work for a site that often get's attacked by bot networks. We have started to use this tool: http://deflate.medialayer.com/ which auto-bans ip's that have more open connections than the set value. By default it's set to 150, we are currently using 250. I would like to know, how low is safe so that search bots and normal visitors do not get blocked? (HowTos)