Except for the Pentium, I can tell the age from the number. The i3 is probably the fastest, but since stuff uses less power these days, there's a small chance the old i5 is faster. I'd look up benchmarks if about to make a purchase. Is the Pentium equivalent in age to 7th gen core i, or is their numbering different?

Now consider that you are an average person, not so tech-savvy, don't really follow CPU industry news.

How would you differentiate?

These aren't realistic choices unless you are buying a used PC. But even less savy consumers understand generations, if you present a fast 1st gen model versus a not the fastest 11th gen model I think the majority will go with the newer model.

So which of these is faster Macbook Air or Macbook Air?

Those are all fast(to the extent matters to their marketing)