Interesting report on the Cycling Weekly website.
Quoting an excerpt from the article (by writer/guinea pig Joe Baker; Mike Twelves was the aerodynamics engineer who ran the tests), where he discusses the most extreme position tested:
"Our final test runs gave us the opportunity to experiment with an extreme body position, using the narrow 30cm handlebar. We tested the aggressive drops position against an extreme ‘shrug’ position at 45kph and 55kph. The goal here was to show how a narrow bar can facilitate a more aerodynamic body position, albeit with some training - and it didn’t disappoint. At 45kph, the shrug position saved a further 24.7 watts compared to the aggressive drop position, and at 55kph, this grew to 42.6 watts. Compare that to the baseline handlebar, and you’ll find a nearly 70-watt saving.
"Twelves and I agreed that this was not a position you could hold for long periods of time, at least not without a lot of yoga and a very good chiropractor. Yet for short periods, it can be a lethal weapon in races."
(Warning: the writer semi-jokingly jeers at the idea of running 42-cm-wide handlebars on a racing bike in the first paragraph.)