OP - I'm just sharing my story with you.... I'm running about 30% antifreeze and 70% distill water and that's because summer afternoons here in TX get reeeeally hot. However in December I drove my car when it was like 22 degress out and the needle never passed the 11 O'clock mark. The car took about 15 mins to reach that temp or mark, but now we know why. when I got my destination, I sat in the car with the engine running and the needle tried to creep to 11:30 :-) but it would slowly come back to the 11 mark.
Currently my boiling point is around 250 degrees compared to the 280+ that BMW recommends or likes to keep our cars.
Now - if you used tap water, that's bad news for you unless you are planning to sell the car soon. If not, I would flush the engine at least another 3 times with 50/50 to get all of those minerals out of your cooling system.
If you still want to run less antifreeze after few flushes then add distill water. Each gallon is like $2.oo. Remember the water pump needs some lubricants from the antifreeze other wise it will break soon.
Good luck!