Okay, s'pose I better make a serious post here...
I happened to be browsing thru Annex 14 today and can confirm the basics of the post by Fr O'Blivien. The design standard calls for a minimum turn angle of 25 degrees, a maximum angle of 45 degrees and an optimum angle of 30 degrees. All of this is only intended to provide flexibility in the design of these things, if needed.
There are maximum speeds quoted which accord pretty much with what Fr O'Blivien posted as well. But remember that these are simply design standards - aircraft speed can always be lower than that, without any problem. Again, it's all intended to provide design flexibility to cater for most situations.