Understandably, with all its power, the SZ791N cannot possibly adhere to Energy Star 4.0 requirements. It's not EPEAT-certified either, but Sony is adamant about not using hazardous materials in the production of its laptops, so it is RoHS-compliant. On our own energy usage tests with a Kill A Watt meter, the system recorded 23 watts in idle mode and 1W in sleep mode. Obviously, it's not as energy-efficient as the low-powered processors in the MacBook Air and the Fujitsu P8010, but it consumed less wattage than its standard-voltage counterparts: The ASUS U6S recorded 26 watts in idle mode, the Acer Ferrari 110034 watts.
It outperformed the ASUS U6S and its Merom processor by 13 percent on SYSmark 2007 Preview Overall, where its performance was boosted by the 4GB of RAM.The SZ791N produced the fastest Adobe Photoshop CS3 scores to date, In all fairness, the MacBook Air and the Fujitsu P8010 use low-powered processors; this explains why the SZ791N was able to run away with top video-encoding and 3D-rendering (CineBench R10) scores as well.

The SZ791N is the first ultraportable to show up on our bench with an Intel Penryn processor, the 2.5-GHz Core 2 Duo T9300. The processor alone helped propel the SZ791N above the competition, delivering outstanding benchmark test scores. besting the U6S by 19 percent and the MacBook Air by 41 percent. Heavy-duty tasks such as photo rendering and video encoding will be a lot faster on this ultraportable than on the MacBook Air or the ASUS U6S.

The SZ791N runs two separate graphics systems, an arrangement unique to the SZ series. A physical switch above the keyboard lets you choose between the nVidia chipset and the Intel Graphics Media Accelerator X3100,

The SZ791N continues to be one of the few ultraportables that run discrete graphics. The nVidia GeForce 8400M GS chipset lets you run many current 3D gaming titles, although you'll need a much better card to run games like Crysis and World in Conflict. Even so, the SZ791N delivered the best gaming numbers among ultraportables with discrete graphics, which include the ASUS U6S and the Dell M1330. otherwise known as integrated graphics.

MobileMark 2007 tests tallied 3 hours 49 minutes of battery life with its 63-Wh battery. The previous model, the Sony VAIO VGN-SZ370P, scored only 2:43. The improvement in battery life results from the Penryn processor core's greater energy efficiency. If you select the integrated graphics, battery life gets an additional hour and 17 minutes, for a total of 5 hours 6 minutes, according to MobileMark 2007—though you get a performance hit on 3D content.