It's almost always surprising and appreciated when a company releases a new version of an OS and its efficiency has increased instead of its bloat. For the most part, it seems like new releases of software just tend to pile on more features and slow things down. Luckily, the new Android 4.3 running on the Nexus 4 seems to do the former rather than the later. Some benchmarks performed on the newly leaked Android 4.3 for the Nexus 4 actually shows improved performance, by a small margin. Here's a quick quote with the details,

Or rather, it seems to improve most of the benchmarks for the device. A Nexus 4 running Android 4.2.2 did best the same device running Android 4.3 in CFBench -Native by a slight margin, but that was to be expected. CFBench - Java showed Android 4.3 improve results by over 500 points.

Android 4.3 supports OpenGL 3.0, and that seems to have helped improve GLBenchmark 2.5 test results by 5 frames onscreen, and 6 frames for the off-screen test.
It's important to note that this particular version of Android 4.3 is still not completely ready prime time because it is missing a few key features. Still, most of what needs to be added shouldn't affect the performance much. Obviously, these changes will likely not be obvious in real-world usage, but it's still great to see progress moving forward and not backward.

Source: PhoneArena