In my opinion until you can reliably put all ten shots into the black and preferibly in the 8 ring you are wasting your time worring about what pellets you use. Its not a rifle where a good group is a one hole group.
If you take the logic of the othe other posters to the extreme I would ask why you are wasting your time with a Tau 7 and not using a Steyr Evo 10e.
Just enjoy your shooting and concentrate on the your sight picture and trigger release they are 100 times as important as the pellet you use.