It has been known that the X86 64bit architecture outperform 32bit architecture. However, little is known whether 64-bit Ubuntu installation outperforms its 32-bit counterpart significantly as the latter is marked as recommended download from Ubuntu website.
Luckily [Phoronix] had answered these questions for us. In its latest article, [Phoronix] compares the performance between 64-bit Ubuntu installation and 32-bit Ubuntu installation on a Intel Core i5 2520 (4 cores) with 4GB RAM.
Audio File Encoding Performance (less is better)
Server Workload Performance (more is better)
The result concludes that Ubuntu 12.10 64-bit performs better on overall compared to 32-bit, especially on video/audio encoding/decoding tasks. Ubuntu 12.10 also performs better with server workloads.
My thoughts:
Although Canonical still marks Ubuntu 12.10 32-bit as the recommended download. It seems that 64-bit installation offers greater performance even without the advantage of having greater memory. Some might argue that PAE still allows 32-bit Ubuntu to access more than 4GB RAM, PAE access on 32-bit is still significantly slower when compared to 64-bit memory access. Personally, I use Ubuntu 64bit for my development machine as all of my hardware has opensource drivers.
The speed increase in x64 with media tasks is most likely because of the additional registers in x64. http://en.wikipedia.org/wiki/X86-64#Architectural_features
Also, read this:
http://en.wikipedia.org/wiki/X32_ABI