However, the likely disposal for a driver for the speeding offence will be the offer of a course (provided he has not done one in the previous three years). This will cost around £100 and a few hours of his time, but no endorsement or points will be involved.
Any repercussions of nominating the driver most likely to have been driving are extremely slim. Strictly speaking, doing that does not meet the requirements of the request – you are asked to identify the driver, not the person most likely to have been the driver. But it is a pragmatic solution employed by many people on here, especially where only individuals are concerned and the likely outcome for one of them is six points.
If the nominated driver accepts that he was the driver, and responds to his own NIP admitting to being the driver within 3 months of the unstated date of the alleged offence, then pragmatism would seem to work, although I would be wary of advising someone to make a potentially false statement.
However, if the likelihood of an out of court disposal encourages clarity of recollection. then that would be a positive. As regards there being no downside to pragmatism, Constance Briscoe's friend might disagree (although that case went far beyond "pragmatism", but did serve as a cautionary tale never to take legal advice from Constance Briscoe).