What is the max amount of runs able to be scored from one over of Test cricket.

It is used to calculate runs required to be made by the chasing team in the case of any interruption in the game of cricket.

I play district cricket, but want to get up to County level. I am a wicket keeper batsman but i am quite short. I wanted to know if anyone can help me. Any tips on scoring runs if you are short
Thanks Spike

India concedes way too many runs in the last 10 to 15 overs (overs 35 to 50) to the Aussies.
Often the run rate becomes around 9 to 10 an over, in the last 10 overs for Australia. The indian bowlers either get too tired after 40 overs or they simply give up, but i do not know for sure why. This is a grave concern, for Indian cricket team against Australia.
Why does this happen? I cannot seem to figure out.