Sub-2hr marathon with a high-tech bicycle pacer?

[guru]

Garmins are entirely adequate. I just got back from a 15km run and used mine to come within 20 seconds of target time.

Exactly. No need for pace bikes, or vehicles, or even rabbits for that matter. When I do time trials(bike), I set the data field to avg mph. That's all I need to know to arrive at the finish at my goal time, while knowing my pace every pedal stroke of the way .