oratory1990's measurement looks generally similar, at a 'high level' view
View attachment 124268
Those are old pads version measurements. 2020 version with pad revision :
https://www.dropbox.com/s/j8r9im6d3s5zglk/Hifiman Sundara (revised earpads, preliminary).pdf?dl=0 , but oratory1990 only made the EQ for this version, not measurements.
But THE question remains... Is Sundara's performance-vs-price worth upgrading from HE400i (2020)?
Sundara's are more detailed, better build, better comfort, slams harder, later bass roll off. Ok-ish without EQ except for sub-bass related music genres.
HE-400i 2020 have a better soundstage (lateral and front) and better instrument separation. Better imaging too. Pretty cool with oratory1990 EQ (with taste adjusted bass shelf), very weak bass with no EQ.
Both benefits medium EQ for single vocalist tracks.
With EQ HE-400i 2020 are better than HE-4XX (in technical abilities). Comfort and bass (without EQ) are better on HE-4XX.
With no EQ, Sennheiser 560s are better allrounders IMAO (I mean better balance in compromises, and better non EQ FR), even if they don't reach resolving ability/details of the Sundara, nor the soundstage/imaging/separation qualities of the HE-400i 2020. They're very natural sounding. Soundstage is a bit weird on 560s (on Sundara too).
So to subjectively answer the question, I'll stick with EQed HE-400i 2020, I find myself listening to them much more than the Sundara, the soundstage/imaging/separation benefits of the HE-400i make
my listening experience much more enjoyable than the extra details of the Sundara.