I always struggle to spend more than ~$400 on a pair of headphones, as I think it's severely diminishing returns after that. Hoping someone has tested both, or owns both and can share impressions.
A year or two ago, I did extensive A/B comparison of the Noire (Aeon 2) to the Closed X (RT re-brand for Drop distribution channel). They were level-matched comparisons and both 'phones were EQ'd to Harman/Oratory, but they were sighted comparisons. I spent too many hours comparing them. I understand this was subjective, but I also spent a year using the same two headphones on the same well-known-to-me music and source electronics. I don't know if the differences would be material enough for you to pay more for Aeon 2 technology (re-designed drivers and maybe some other tweaks to bring out soundstage) over Aeon 1 (RT) tech, but it was enough for me, even though I loved both headphones. I posted my detailed reactions on another thread then, but I can summarize here.
For me, the largest difference was in the soundstage. The Closed X is perceptually mostly between my ears, while the Noire has a larger stage outside my head. This was not always a very large soundstage, but with well-recorded, acoustic material that used good miking technique, the subjective space (including delay, reverb, etc) could be pretty large. For me, this was and is a dramatic difference, but at the same time, this kind of thing varies by listener more than other perceptual attributes, and listeners vary a lot in how much they care about it. All I can say is that over half my listening is of acoustic sources, and it is a material difference for me with these headphones. With the Noire, I had a good number of recordings where I felt like I was not far back in the audience in center stage; but rarely so for the Closed X.
(Although most comparisons were EQ'd to Harman for both phones, I also did comparisons without EQ because of Dan Clark's comments about tuning the Noire's FR for to create more recessed mid's as a means to create a more realistic soundstage. I think that is true, but I also had a similar perception even
with common EQ. This is a complex subject, and probably a rabbit-hole. Go figure; we're well into subjective listening here.)
The other persistent difference involved two aspects of a single characteristic, that of separation. I have a good number of reference recordings that I use to evaluate separation. Some of them are, for example, orchestral, jazz or other recordings with congested, overlapping instrumental lines, while others were instrument-by-instrument comparisons of percussive transients (e.g. wood-on-wood effects, rimshots, etc.), or simpler, overlapping instrumental lines (e.g. bass viol, drums, sax and piano). Both the Closed X/RT and the Noire/Aeon 2 were very good in instrumental separation, but the Noire was better, and it seemed associated with a subjective characteristic that some call instrumental "decay". For example, the wood-on-wood had a more realistic reverberance or timbre as each transient decayed, while the Closed X sounded more damped. A very recessed bass line in a jazz ensemble recording was easier to pick out clearly with the Noire. The sense of a drumstrike propagating on a drumhead was a bit more realistic with the Noire. A very congested opening movement on a Brahms Piano concerto, that always gives my playback sources at least a little trouble, came through pretty well (I used to blame the recording, but my best sources can navigate it).
The differences that I heard, if others also hear them, probably are more relevant to someone who listens to classical, jazz, folk, or other acoustic sources. The Closed X/RT and Noire/Aeon 2 have more in common than they are different. They both have deep, clean bass and great separation, I could take either to a desert island; but found the Noire to fit my acoustic preferences somewhat better. If you are mostly an "experiential" listener, who focuses on the musical experience, you might not notice the differences because of the dominant similarities. But if you are sometimes also an "analytical" listener, who dwells on the audiophile experience, you might sensitize yourself to the aspects I noticed. Anyway, I recently sold the Closed X for $275 and when I originally got the Noire, I used the DCA Club 15% discount; so the financial pain of upgrading to the Noire was softened. a bit.