The FX has the potential to be a fast processor in specific workloads. Yes, that fits to what you said. Certainly not when single-threaded, but in multi-threaded workloads it can still be fast. But faster than the i5 it is only very rarely (which, yes, is less harsh on the FX than I was in the comment above). It is a pity that its potential (4 years ago it compared to a weaker i5) could not be used in meaningful ways in common software.
By now it is clearly not a good choice anymore: It uses more energy, depending on what you compare it with it is more expensive or costing the same, and it is on an old platform (AM3+) that won't see further updates.
> They're evenly matched on other tests (e.g. Handbrake & "Agisoft PhotoScan
No. We don't seem to have the same benchmarks. I'm looking at http://www.anandtech.com/bench/product/1709?vs=1646, where the i5 is clearly faster in the Agisoft and Handbrake benchmarks. It is mainly in the artificial multi-threaded benchmarks as well as Linux 7zip and Linux OpenSSL that the FX can win. For games the FX is almost always behind, but often close, however, those are partly limited by the gpu and thus not too meaningful.
> If those results are accurate, they do seem to support that AMD FX CPUs are still competitive with new Intel CPUs in the same price range.
No. They mean get an i5: Way better in single threaded workloads which is what counts for 90% of software, faster in realistic multi-threaded workloads. Get an FX if all you do is run OpenSSL and 7zip under Linux, or if already having a good AM3+ board (for that scenario it still is good enough).