The basic deal is............the answer to your problem IS THERE to be found on Google. If you don't start your thread as having exhausted the searches on Google that you can think of the responders are left to wonder-----if it isn't worth your time to type questions, why is it worth their time to type answers to questions that can be found with ease and a true desire to find them.

Besides when a Roadie changes from the 4th to the 7th cog on their cassette their chainline is off more than the 5mm you say your's is off. I don't see a bunch of geared bike riders along the roadways dicking with their bottom brackets because of that.

Ride your 5mm for a while and see if it really matters.

Besides, the real reason it isn't perfect is because the world is round.