It wouldn't surprise me to discover that Google's team did lots of their own performance tweaking and tuning to compensate for their disadvantage. I do love the responsiveness. Now their Gmail app on the other hand was painful for me to use.

Yeah I could never really tell how that even made it to the App Store. Some stupid wrapper around the web page, but the Chrome app is definitely more along the lines of what I'd expect from Google.

The latest update to the GMail app for iOS is vastly improved.

How does it compare to Sparrow?

These tests are only JavaScript benchmarks and don't reflect real-world usage well. Chrome for iOS has a custom network stack and (like someone else said) page prefetching among other things.

It supports SPDY which could make a significant difference at least for Google services.

The snappiness could be because iOS Chrome pre-fetches pages if you're on a wifi network. A lot of the lag of Safari on iOS seems to be in the actual fetching of pages.