Very important to keep in mind that the performance "rules" are based on, and make the presumption of, some set of standardised conditions.
If well on one side or the other of whatever switch point is relevant (Vef for a critical reject), things are fairly easy. If at the switch point then, for a critical runway in this case, everything is based on real world conditions reasonably approximating standardised certification conditions .. otherwise the end result may involve some tears.
A dynamic V1 exceedance during a critical reject is pretty well guaranteed and is part and parcel of the AFM data .. one ought not to worry too much about that distraction. Main thing is that the initial reject action be commenced not later than V1 for there to be a reasonable probability of matching the AFM figures. SOPs are based on probable outcomes .. in general, the normal stop/go decision will give the better probability of a successful outcome.
If, on the other hand, something else significant happens during the exercise and is not covered by the certification assumptions, then the commander is well and truly on his Pat Malone and makes whatever decision appears best at the time ... One example we talk of from time to time is the min weight, min speed schedule critical failure in the presence of a strong crosswind. There is a good chance that the aircraft will be out of control directionally and keeping going is not a sensible option ... a case where a reject decision above V1 may be the only sensible option.