Some research has reported the optimal drinking temperatures to be around 60 degrees C (plus/minus 8.3 degrees C to include the preference for roughly 68% of the population because not everyone agrees on a temperature. Of course there are still outliers; a friend of mine drinks at 78 degrees C!).
Previous research (I can’t find the actual research paper) showed that 2 minute brewing + 6 minute cooling would get you the perfect drinking temperature of 60 degrees C. My home brewed experiments suggested that – 1. there is a inter-flat variation, 2. it’s hard to control for room temperature/mug used…etc. .
So the experiment suggests that the difference between milk before or afterwards has only the smallest of effects, even smaller than room temperature. So, probably best to just not worry and drink your tea!
Optimal drinking temperature for hot beverages: http://www.ncbi.nlm.nih.gov/pubmed/18226454
To make a perfect cup of tea: http://www.telegraph.co.uk/foodanddrink/foodanddrinknews/11415372/Is-this-how-to-make-the-perfect-cup-of-tea.html