I want to acknowledge the points of @8&8 and @Tridents in a general way and knowing now that XDA Developers is the source of the claim that the Snapdragon 8cx Gen 3 CPU is composed of X1 and A78 cores alone, I don't want to pit myself against that.
Still, here is the way I came at the issue. I considered a single threaded Geekbench score of 730 to be representative of the Snapdragon 8cx Gen 2. A 40% increase on that, as it happens, squares very nicely with the early benchmark numbers we are seeing in the Geekbench database for the new chip. It is obviously wrong to say, as you seem to be saying @Tridents, that, on current indications, an X1 core at 3.0GHz would be likely to return a single threaded GB5 score of 1025, say, when X1 cores at 2.8GHz already return better results than that. It was those benchmark results that made me think the A78 was the more likely candidate and if the scores don't shift upwards from where they are now the A78 would still look rather likely.
I note that Windows Central has offered a GB5 single threaded score for the SD8cx Gen 2 of 797 as more representative. So, if that number is right we can expect to see single threaded GB5 scores for the Gen 3 SoC that exceed 1100. The A78 at 3GHz, it should be noted, couldn't post such a high score. That said, scores in the low 1100s would still be abysmally low for the X1 SoC at 3GHz. That is in the vicinity that the X1 at 2.8GHz already scores today. Of course the 5LPE process just isn't up to it.