Oil filter by-pass pressure setting

["Al McMillan" <mgbfan@hotmail.com>]

I have looked everywhere in town (Winnipeg, Manitoba) for Mann 917 filters 
but no luck. One of the distributors cross referenced to a Baldwin B163 
filter which has the anti-backflow feature, but is rated at 8 psi by-pass 
pressure as opposed to what they said was normal for North American cars at 
13-15 psi. Is this a signifigant difference for use in my summer driven B ? 
An explanation would be appreciated.
Al McMillan