Surely, the time for making all these decisions is before you brief the TO, while working out the speeds. At that point, if you notice that you have excess runway length, then you can (if the data exists to permit it) select a nice high V1 if you so desire, and work out in a nice calm atmosphere that you do, indeed, have the runway, brake energy, etc. to do so. Then you can brief that V1, and fly to it.
But having picked the V1 and briefed it, you've made your choice.