Re: Spectre on the hyperthreads
There are a number of processor architectures that have taken things further than the Xeon 2 threads per core model. Off the top of my head the Sparc T1 had 4 threads per core, rising to 8 threads/core by the time we got the T3.
In current use, the XMOS processors use this technique, I think there are between 4 and 8 round robin slots per physical core, so the 500Mhz processor appears to run 4 independent threads at 125Mhz, for example (which is handy, as it hides fetch latency etc).
If you are writing memory bound software, hyperthreading isn't a win. If you are compute heavy, it can help, and of course it really depends on what else is running on the cores (outside your control).