Just adding my experience and benchmarks to the thread - and say thanks for bringing it to my attention.
My
IPhone 6S - was ok on IOS 10 but 11.1.1 brought the phone to a crawl
- I suspect it was at this point my cpu was throttled.
Battery was still ok - lasting the day, sometimes more - but phone was slow.
I did a full DFU reformat and reinstall from scratch (not restore) - didnt help.
I put it down to OS bloat and was planning reluctantly to upgrade to IPhone8...(yeah not X - Id miss the fingerprint scanner)
On reading this forum last night - I ran benchmarks...
Geekbench 4:
1054sc/1770mc (high power mode) (sorry, didnt run in low power mode)
CPUDasherX:
600Mhz when charged (& same 600Mhz in low power mode)
Battery replaced this morning (free from Apple

)
and same phone after battery change...
Geekbench 4:
2544sc/4433mc (& 1462/2485 low power)
CPUDasherX:
1848Mhz (& 911Mhz in low power mode)
And its like new again...
I have screenshots.. but above is whats on them.
Notes and terminology from Apple:
* Apple Support call said their diagnostic software flagged the battery as "
Consumed"
* Apple repair center said it had
416 recharge cycles - so not that many but within the 400 to 600 they expected for a 6S.