Okay, I completed my testing. I don't have a Z on motherboard to run vs a Z on riser, so I just used my X to see how it would go down with a high memory scene.
And you know what I found? Even with the X, I had a hard assembling a 6GB memory scene. I used 5 G3F characters, a background, and 4 of 5 had clothes. So I guess one could say, well add a 6th then to push it over 6 GB, test with a Z, and see how it works with the OOC. But Daz gets so damn slow, even with the X and its 12 GB memory, as I closed in on 6GB, that it wasn't even worth it for me at this point. I can't even navigate the app, let alone the OcDS plugin at that level. I did run a test, though, and this is what I recorded. Don't know if it serves any purpose, don't think it ever used OOC.

- OcDS with no OOC

- OOC Settings

- OcDS with OOC
But I can totally imagine that a 3GB card would break down under the weight, and add that it's on a riser at 1x, it would crack. And from what I am seeing, OOC is not going to be as optimized as we would like.
But, I mean, forget it....It's so slow it's unusable at the 6GB level, and my scene didn't even need OOC. And even if I could mirror your results with a Z on motherboard vs Z on Amfeltec, what does that do, just confirms what I already know. It's slow as F^@% either way...
Hey, how do you navigate a scene on Daz at that memory level, wireframe? Shutting off stuff in the scene editor? (ie - hair)...let me know if there is a way to speed things up in the app itself without sacrificing texture, polygon count etc.
To any non-DAZ users, long story short, not only are you battling a riser, but a app and respective OR plugin that is super slow at 5-6 GB texture levels. In fact, probably would be too slow with a 32 GB Pascal...Well, maybe not, but for me with the X, too slow no matter what at this level.
But here's my silver lining,I did learn something. I did export the scene from DAZ as an .obj mesh and then loaded that mesh into the OR standalone, and then I did not have to deal with the DAZ app's crawl. Felt much smoother to work with. I thinkl the conversion compressed something, looked like it was less memory...Here is my render at same res, higher speed than the plugin. I don't know if that extra process matters to you, but render time was faster 0:57 vs 3:14, same 2560 x 1440 resolution, tried to mirror all lighting elements.

- OR Standalone
Sorry to be such a Daz grouch. Okay, here is the finished image (done in standalone)
BTW, I just loaded it in sloppy, for testing purposes...nah, just kidding, I worked super hard on every detail so that I would 'Tantalize' you...:

- The final test to enter the 'League of Tan' is the Tan Challenge