Statistically, having a pacemaker makes no significant difference.
That is the findings of recent research from South Africa. In a study entitled 'The Effect of a Second Runner on Pacing Strategy and RPE during a Running Time Trial'.
For the study 11 club runners with 5km times of around 20 minutes carried out a series of 5 time trials over a three week period. They ran the first and last time trial on their own and the middle three with a pace maker. Of the trials with a pacemaker, one was ran with the pacemaker slightly in front, one with the pacemaker slightly behind and the other with the pacemaker alongside. In all cases the pacemakers were faster over the 5km than the subjects.
The results found that although the subjects felt that the pacemaker had helped them run faster, the results showed no significant difference for performance, heart rate or perceived exertion and concluded that "These findings indicate that an athlete's subconscious pacing strategy is robust" and therefore not helped by another nearby runner.
So although, statistically the results show "no significant difference" looking at the average times ran(see below) I would rather be running the faster times.
Average times ran by the 11 runners:
First solo time trial 20.26
Pacer in front 19.57
Pacer behind 20.10
Pacer at side 20.24
Second solo trial 20.03