I personally make it pretty high, like 20:20 or so. That will catch flood bots, and yet allow most pastes to the channel. If you have a problem with people flooding useless junk or just being annoying, setting it lower will have them kicked sooner, but then again kick people who 'shouldnt' be kicked.
5:8 and close settings to that are fine for most channels that I've seen, but look out if you paste more than five lines! I have a lot of users in my channels that paste articles, ask for help with issues, etc, and its annoying to have to ask the last line the channel saw to resume the paste.
or if u want to paste a lot of stuff i use the setting 50:60 but only use this if u run a channel that needs pasting for example #bothelp (people pasting there whole ps aux)