Ubuntu 11.04: i686 vs. i686 PAE vs. x86_64
The LZMA compression performance was improved by about 10% with the x86_64 kernel.
Using a 32-bit kernel with Physical Address Extension did not cause any change for the Core 2 Duo notebook but it did with the Core i7 notebook, likely because the PBZIP2 test can take advantage of the extra memory. The 64-bit setup though offered the best performance with the Core 2 Duo and Core i7 systems both being about 30% faster.
With the multi-threaded C-Ray ray-tracing benchmark, enabling PAE didn't provide any benefit for the ThinkPad T61 notebook with 4GB of memory, but it did provide a 10% performance boost for the Core i7 notebook with four cores (plus Hyper Threading) and 8GB of RAM. The x86_64 configuration was more than twice as fast for the Core 2 Duo notebook while the Core i7 notebook was enhanced by just under 40% with the 64-bit kernel.