Benchmarking Yafray on AMD64 X2 4200+ and Pentium 4 HT 3GHz

Did a benchmark on Yafray, a rendering software, recently on several cases. See the plot below,

Running in 64bit helps quite a bit in the performance. However, it's not clear if it is due to the use of different compilers.

For AMD64 running 64bit, I use GCC 4.1.1 64bit.
For AMD64 running 32bit, the compiler is unknown as I use the rpm provided by yafray.org.
For Pentium IV, I use GCC 4.1.1 32bit.

Overall, it should be fare enough to compare AMD64 64bit and Pentium IV 32bit since they are using the same compiler.