Hmm everywhere I'm looking, it looks like the general consensus is that stock 1156's put out roughly 400 lumens.
Khoalty does seem to make bigger promises than other sources so far, with their regular LED 1156/7507 quoted to put out 360 lumens, and their switchback bulbs putting out more than 400 lumens.
Tempted to try them out...
I personally think THESE look promising..
^E60 5 series pre-LCI requires 7507's too. If this guy was able to use these 1156's, I think theres a good chance we can too.