Re the test strips and the pH-meter :
Test strips 7.85 +- 0.20
pH meter 8.05 +- 0.15

Your test strips was definitely NOT significantly off, there is not anything in the whole world that is an EXACT measure, especially when it comes to pH measurements, electrode, exact mix, temperature.... a lot of stuff enters the equation here.

I'd say your reasoning from the start based on the test strips was sound, and that you was in the ball park all the time.