Rosberg topped the final day of the test, during which Mercedes-engined teams dominated the timesheets.
Rosberg's final benchmark of 1m33.283s put him within a second of his own pole time from last year's race at the same venue.
However, the team did find a number of issues with the F1 W05 over the course of the test, showing that even the more comfortable teams are not immune to the difficulties of mastering this new formula.
While there were plenty of positives for the four Mercedes-powered squads (Williams was so advanced in its programme that it spent day three doing pitstop practice, while McLaren set top-four times on each day with Magnussen and Jenson Button driving), there was more disquiet at Renault outfit Red Bull.
The team suffered problems with its RB10 throughout the test, limiting Daniel Ricciardo and world champion Sebastian Vettel to a combined total of 116 laps, with a best lap time of 1m39.837s set by Ricciardo on the final day.
By contrast, Rosberg's best lap time of the week was over 6.5 seconds faster, while Mercedes completed a grand total of 315 laps between its two drivers.
The other Renault-powered teams encountered plenty of difficulties too.
Lotus looked in deep trouble early on, and Romain Grosjean cut a dejected figure in the paddock during the first two days.
Bahrain F1 test in pictures
But 59 laps for Pastor Maldonado on the final day (which still featured plenty of technical issues) gave the team cause for greater optimism.
"Major" technical problems for Toro Rosso, and Caterham only logging decent mileage by turning the engine down on days one and three, made for many a furrowed brow among the other teams using Renault propulsion.
Meanwhile, Ferrari completed a solid if unspectacular amount of running with Fernando Alonso and Kimi Raikkonen.
The Scuderia amassed nearly 300 laps across four days, despite a telemetry issue restricting Raikkonen to just 44 laps on Friday before he crashed the car at the end of the final day.
Apart from Esteban Gutierrez (who racked up 151 laps and set the eighth fastest time of the test), drivers in the Ferrari customer teams endured a difficult test.
The Mexican's team-mate Adrian Sutil clocked 82 laps on day one, but only seven on the final day, when the Swiss team discovered a chassis problem on the C33.
Marussia arguably endured the worst test of all the teams, completing less than 30 laps across four days, thanks to IT, engine and fuel system difficulties.