panel smackdown question

[Naptown]

But that's not because of improved efficiency, right? It's mostly just larger panels (more collection area).

Even so, it still gives economies for installation (fewer bolts to tighten, fewer electrical connections).

Actually both but mostly from increases in efficiency.
5 years ago it was hard to find a 60 cell panel over 240W
Now 270 and up are the norm all the way up to 300W
Sunpower's tend to be 96 cells and about 4" wider and 5 inches shorter than most 60 cell panels.