I'm about to make a new Linux install, which will be primarily used for programming. I've seen benchmarks showing speed improvement of 64-bit version, however, I have hard time of telling how much these benchmarks translate to improvement in every day usage. And of course there are other aspects to consider.

Usage I have in mind:

• mainly programming Python, with occasional C, C++ and Java;
• IDEs, which are using Java platforms (Eclipse and IntelliJ);
• on very rare occasions having to compile for 32-bit platform;
• not planning to have more than 64GB of RAM anytime soon (and I don't mind using PAE kernels);
• machine in question has 4GB RAM and Athlon II X2;

What are pros and cons of choosing either i386 or x86_64 distro?