I was thinking about this as well, and there are a few data points we can use to estimate the difference between Samsung's 8N process and TSMC's N6. On the transistor density side it's fairly easy to estimate, as we know that all of Nvidia's Ampere parts have come in at around 45MT/mm2, with
Orin coming in at 45.6MT/mm2, so it's extremely likely that Dane will have a similar density if and when it's manufactured on 8nm. Meanwhile, I'm not aware of any actual transistor density measurements from N6 chips, but
TSMC claim that it offers 18% higher density than their (non-EUV) N7 process. Nvidia manufacture the A100 GPU on the N7 process, and it
comes in at 65.6MT/mm2, so we could estimate that a Nvidia chip on N6 would hit around 77.4MT/mm2. This is about 70% higher transistor density than they're getting on Samsung 8N. Of course the density scaling might not be exactly what TSMC claim, and a gaming SoC may not line up exactly in logic density with a HPC GPU, but it's probably a reasonably close estimate.
For power consumption it's a bit trickier. We do have the Mediatek Dimensity 1100 and 1200, and the Qualcomm Snapdragon 778G phone SoCs, which are manufactured on N6 and feature A78 CPU cores, but it's difficult to get precise power measurements for them. I found reviews of phones featuring the Dimensity 1200 and Snapdragon 778G including power measurements during Geekbench runs
here and
here. However these are full system power measurements, and due to the unclear testing methodology (they don't specify whether it's single-core or multi-core Geekbench) and seeming inconsistencies (eg the lower-clocked 778G based phone seeing much larger power consumption spikes than the higher-clocked Dimensity 1200 based phone), it's not really enough to make any conclusions from, unfortunately.