You could install to one of the Athlons, then copy it to the other two > Athlons and one of the FX machines. Then, reconfigure the FX install > for more CPUs and native -march, recompile world and copy it to the > other two FX machines. >
Even that might not be worth it. Unless you're using something that benefits from the new instructions in the FXes, or requires the last .1% performance, a single install on an Athlon and copy onto the remaining 5 systems will give you more time for something else. From a support point of view the consistency can be a win. Just remember to specify the Althlon64 CPU type in the kernel config, but with 8 cores max. For the hardware, just select a superset of the two systems requirements in your kernel config. If you build as modules any superfluous code wont even be loaded.
