Would be super cool if you (and someone else?) could write how your Reference 6950 XT behaves
Hmm, well, here's what I have between my personal system and some work systems:
1 6900 XT AMD reference on a z690 ProArt, 2xDP running 5k LG UF + 1x HDMI running 4k LG scaled, idles 50-58c
1 6900 XT AMD reference on a z790 ProArt, 2xDP running 2x 4k LG both scaled, idles, 41-48c
1 6950 XT AMD reference spoofed on a z390 Designare, running 1x 4k scaled, 1x HD, idles 40-45c
All three have zero-fan behavior until pushed. All three have NO OC DP definitions. All three report Metal 3 in System Information, but only the 6900s cosmetically report as the cards they are in "About This Mac," the 6950 reports as Navi 21 -- as I mentioned before. I did a bunch of testing to discern if DP definitions (or SSDT definitions) had any effect, and this is what I settled on.
I don't find GB to be a tremendously accurate bench test, in fact, if you monitor GPU usage (through either activity monitor or GPU monitor) you'll see it's hardly hitting the card, PLUS, the results can be wildly variable. That said, the 6900s on the z690/z790 can report 211k to 235k. The 6950 on the z390 can report SLIGHTLY higher, sometimes. Is it the tiny amount of higher clocks? Or are the tiny amount of higher clocks impacted by the GEN 3 bus? Who knows.
Cinebench is a decent GPU bench as it hits the GPU harder, but results vary run-to-run just like GB. I ran v2024 last night for you on all three machines (2x SMBIOS MacPro7,1, 1x iMacPro1,1), and one just prior to updating to Sonoma from Ventura and here are the results:
6900xt #1 on z690 Ventura = 8644
6900xt #1 on z690 Sonoma = 7928
6900xt #2 on z790 Sonoma = 7643 (I imagine having 2x 4k scaled to 2560 is why it's slower)
6950xt on z390 Sonoma = 8304
I use all three machines for video editing purposes, and specifically Resolve, and Resolve can really hit them hard -- so hard, in fact, that all three have been built into cases to specifically help GPU cooling. We can drive the GPUs to as high as 100c territory depending on the rendering. All three crush the typical Resolve benchmarking tests, so much so that we ditched a Cubix expansion chassis with 2x Radeon VIIs + 1 590 internal for GUI in favor of just the one 6950xt.
Hope some of that helps,
J