The best way of giving extra lifespan to SL is to make it work like newer systems as much as possible. All current software for macOS is built and tested against libc++ using clang.
The only reason to use libstdc++ is to get the prebuilt binaries. However there are issues with the gcc headers and differences in the libraries often enough to cause real headaches. As time passes, these issues are getting worse, not better. For this reason, MacPorts will have to force all 10.6 to 10.8 users to use libc++ soon. IMHO, the sooner the better, as fixing libstdc++ issues is really a waste of effort. When we run into troubles now, we just force libc++ behind the scenes in the Portfile. My $0.02. K
