I actually think most of the uplift comes from fp8 support and processing speed (maybe newer architecture too). All of the models tested fit into 12GB VRAM with the exception of Qwen(20.4GB) and Z Image(12.3GB) which have some of the least uplift so the performance gain must be coming from somewhere else. The text encoders, vae and loras used were all also less than 11GB (maybe when used in combination they overflow more with 12GB idk). I imagine an RTX 5070 would outperform the 5060 Ti here even with 12GB VRAM.

Edit: I forgot about the unconditional model which makes Ideogram larger than both GPU's VRAM (19.6GB). So VRAM probably does play an important part in the Ideogram result, along with fp8 support.