The MacBook Air has won over a large number of Apple laptop users. But in order to offer such extreme portability, the MacBook Air comes with a few tradeoffs. One of those tradeoffs is with the flash storage—it’s fast, but it’s expensive, and to keep the cost down, Apple is a bit stingy with the amount of flash storage it makes available in the standard MacBook Air configurations. With the ultra-thin laptop’s storage space ranging from a miniscule 64GB to an underwhelming 256GB, it’s no wonder that some MacBook Air lovers want to increase the capacity, no matter the cost.

If you can afford it, OWC offers storage upgrades for the mid-2010 MacBook Air models. The Mercury Aura Pro Express is available in capacities ranging from 180GB for $470 to a 480GB model for $1580, which is $20 less than the price of the high-end 13-inch MacBook Air with 256GB of flash storage.

(Apple refers to the storage device in the mid-2010 MacBook Air as flash storage, not as a solid-state drive, or SSD. The storage device in the MacBook Air looks similar to a RAM module, but with the connectors on the short edge instead of the long edge. The SSDs available in older MacBook Airs, MacBook Pros, iMacs, and Mac Pros come in a typical 2.5-inch notebook drive package. OWC refers to the Mercury Aura Pro Express as SSDs, though they have a similar design as the flash storage included with the MacBook Air.)

Macworld Lab received a 180GB Mercury Aura Pro Express and installed it in the 11-inch MacBook Air that came with 64GB of flash storage. The installation process is relatively simple (especially when compared to upgrading the iMac’s drive), and OWC provides the necessary tools. Unfortunately, there’s not much that can be done with the stock flash storage once it’s removed, unless someone begins selling an external enclosure.

Once the storage upgrade was installed, we found the added capacity to be a blessing, but our performance results were unexpectedly mixed. The marketing materials for the Mercury Aura Pro Express claim that the drives offer up to 68 percent faster performance than the stock flash storage. In order to see such a vast a difference between the MacBook Air's flash storage and the Mercury Aura Pro Express, we had to use automated tests that task the MacBook Air in ways that most people wouldn't use an ultra-portable. With the AJA System Test, which is used to see how well your system would perform with the AJA hardware working with HD video in real time, we found impressive speed improvements, with the Mercury Aura Pro Express posting 13 percent faster write speeds and 26 percent faster read speeds than the MacBook Air’s stock 64GB flash storage. We also saw up to 47 percent faster average read speeds and 32 percent faster average write speeds using the Fill Disk tests on diglloydTools’ DiskTester.

However, when we tested with Speedmark 6.5, our application-based benchmark suite, the results showed little or no benefit with OWC’s drive. The MacBook Air with the OWC upgrade finished encoding MP3s in iTunes a little more than 5 percent faster than the stock device and exported a movie in iMovie about 3 percent faster. Startup times and Finder tests, like file duplication and unzipping a 2GB folder archive, were actually slower on the OWC than on the MacBook Air with its stock flash storage.

We contacted OWC to discuss our results. The company responded by directing us to test results from other sites, such as Ars Technica, Cult of Mac, and Notebooks.com, which mostly used synthetic tests. Our own synthetic tests showed results that were similar to theirs, but we didn't see the same results in our application tests.

In case you're interested, we recently compared the speed of a flash-storage equipped MacBook Air and the hard drive equipped MacBook Pro.

If you're a MacBook Air user who needs a serious boost to the laptop’s storage capacity, the Mercury Aura Pro Express SSDs are worth a look. But if what you’re looking for is an overall speed boost, our tests suggest that these drives won't have much impact in everyday use.

[James Galbraith is Macworld’s lab director.]