Any decent dyno shop will calibrate the dyno to match the engine rpm based on the gear used for the pull, making the gear selected irrelevant. I was told by my tuner to dyno in 4th, the shop wanted to do 3rd, but I insisted because I was getting logs as well. Having the dyno done in 4th will reduce stress, time under load and be safer all around than trying to dyno in 7th, per my tuner.