I would like to know if there are any documented performance differences between a Python interpreter that I can install from an rpm (or using yum) and a Python interpreter compiled from sources (with a priori well set flags for compilations). 
I am using a Redhat 6.3 machine as Django/Apache/Mod_WSGI production server. I have already properly compiled everything in different setups and in different orders. However, I usually keep the build-dev dependencies on such machine. For some various ego-related (and more or less practical) reasons, I would like to use Python-2.7.3. By default, Redhat comes with Python-2.6.6. I think I could go with it but it would hurt me somehow (I would have to drop and find a replacement for a few libraries and my ego).
However, besides my ego and dependencies, I would like to know what would be the impact in terms of performance for a Django server.
If you compile with the exact same flags that were used to compile the RPM version, you will get a binary that's exactly as fast. And you can get those flags by looking at the RPM's spec file.
However, you can sometimes do better than the pre-built version. For example, you can let the compiler optimize for your specific CPU, instead of for "general 386 compatible" (or whatever the RPM was optimized for). Of course if you don't know what you're doing (or are doing it on purpose), it's always possible to build something slower than the pre-built version, too.
Meanwhile, 2.7.3 is faster in a few areas than 2.6.6. Most of them usually won't affect you, but if they do, they'll probably be a big win.
Finally, for the vast majority of Python code, the speed of the Python interpreter itself isn't relevant to your overall performance or scalability. (And when it is, you probably want to try PyPy, Jython, or IronPython to replace CPython.) This is especially true for a WSGI service. If you're not doing anything slow, Apache will probably be the bottleneck. If you are doing anything slow, it's probably something I/O bound and well outside of Python's control (like reading files).
Ultimately, the only way you can know how much gain you get is by trying it both ways and performance testing. But if you just want a rule of thumb, I'd say expect a 0% gain, and be pleasantly surprised if you get lucky.
Performance differences between python from package and python compiled from source