With the EXT3 file-system there was not much change between the Debian 4.0 and 5.0 releases either on the ThinkPad notebook or with the high-end virtual machine instance. However, when switching from Debian 5.0 to the Debian 6.0 testing snapshot there is a massive drop in performance. There was also a drop between Lenny and Squeeze with the virtual machine, but not by nearly as much. This latest performance drop is likely due to changes within the Linux kernel that affect the EXT3 file-system performance. As shown in our five years of Linux kernel benchmarks, when looking at its Apache performance there was a similar drop in performance for that virtual machine and it happened between the 2.6.29 and 2.6.30 kernels, which is right between Lenny and Squeeze. On real hardware though this drop is much more severe than in a virtual machine.
The PostgreSQL database performance is also down when comparing Debian 4.0 and 6.0 on each system. With the 64-bit virtualized Debian testing the performance was not down as much as when running on real hardware. With the 64-bit testing the performance is also up slightly compared to Debian 5.0 where it is down with the Pentium M laptop.
On the ThinkPad R52 the PostMark performance was massively down with Debian 5.0 before recovering slightly with Debian 6.0. With the 12-thread x86_64 KVM virtualized copy, the Debian 5.0 performance dropped too but it massively jumped with the Debian Squeeze installation to the point it was faster than in Debian 4.0. Our five years of Linux kernel benchmarks demonstrated similar results.
With the C-Ray ray-tracing benchmark there is a massive speed-up between Debian 4.0 and 5.0 and that gain is still there with Debian 6.0. This may be due to optimizations in the updated GCC compiler in Debian 5/6.