I have only skimmed these articles, but they address your question regarding POWER:

https://wiki.raptorcs.com/wiki/Speculative_Execution_Vulnera...

https://www.ibm.com/blogs/psirt/potential-impact-processors-...

https://www.talospace.com/2018/08/l1-terminal-fault-another-...

http://tenfourfox.blogspot.com/2018/07/netspectre-not-much-o...

http://tenfourfox.blogspot.com/2018/01/actual-field-testing-...

http://tenfourfox.blogspot.com/2018/01/more-about-spectre-an...

http://tenfourfox.blogspot.com/2018/01/is-powerpc-susceptibl...

The _Talospace_ and _TenFourFox Development_ articles are by Cameron Kaiser, who is active on HN (and Blogger) as classichasclass.

Edit: Add missing 'and' in last sentence.

Yep, ARM is affected. See this: https://developer.arm.com/support/arm-security-updates/specu...

My understanding is that older A53 implementations of AArch64 / ARM64 are strictly in-order and thus not suceceptible to Spectre etc.

Any CPU with out of order speculative execution is probably vulnerable.