So, If I play at a classical recording (notably symphonies and concertos) at 100-110dB I will hear all the instruments from all the frequencies?
You should be already able to hear them at even 80dB - 90dB listening levels, assuming your headphones have good detail retrieval and dynamics, which I'm not sure if the R70x has.
my definition of neutral is how the FINAL recording was recorded, regardless of if the instruments were mastered naturally. I don't want to color the sound more than they already are. Basically how you hear them in the recording room. Maybe a bit of coloring I don't mind (even my DAC and R70x'es are a bit warm) but I'm not a fan of headphones that drastically color the sound. It's also the least fatiguing for me, the bass/treble of the warmer/colder headphones mess with my head and sometimes give me headaches.
This may be a bit difficult to find because almost all headphones have some sort of colouration, even studio monitors are usually more treble emphasized to find nuances in a recording.
And usually what is uncoloured is person dependent to their baseline of what sounds correct to them. For example, my baseline threshold is the Hifiman HE-500, which to me plays tracks as real to what I hear live instruments and voices would be. For others, it's the HD6XX/HD650. Whereas for me, the HD6XX/HD650 series have that subdued treble that makes the overall presentation a bit unnatural because live performances are played in an open space. This is an unpopular opinion of course.
That being said, you would need to try a lot of headphones to be able to gather this perspective, and taking people's comments online will only give you more confusion with the conflicting opinions.
Regarding the Focals. I'll do more research. They look really nice and are really easy to drive. Only small gripe is that the max freq. is 28kHz. If I see that they're mostly balanced I might consider the Clear or Elear as my endgame option. There's no point of going higher than that.
The Frequency range shouldn't be a factor in your decision making. Anything beyond 20 kHz and below ~8Hz is already inaudible for the average human auditory system, and does not affect the overall audio presentation.
My personal take, the Focal Clear is well-balanced, but not exactly flat neutral. To my ears, they're not really colouring the sound, but have deviations from a "neutral" response that makes them sound correct in pitch and tonality. It has its flaws, such as the slight edginess in consonants if you're really sensitive to that, which fortunately I'm not but some find that annoying.
The Elear has its own flaws, such as the hole in the upper mids that makes certain vocals and instruments in that region muted. But this is not to say that you won't like them. If you can't demo them, you would have to take a chance with gunning for one from a reputable store with a good return policy (i.e. headphones.com).
If you really want the best headphone experience, there is a point going up, such as trying the Susvara or the Orpheus. But of course, that's all relative. All headphones have their own flaws, but I believe those two are TOTL with very little flaws in their overall audio presentation from what I've been reading so far. Whether they're worth their asking price, that's up to you.