Single-core is indeed impressive. It will be interesting to see what people report using it for real-world tasks. I wonder how much you’ll notice the lower multicore performance.
To me, personally, the $400 CPU bump would be worth it. Heck, who am I kidding? I’d go for the TB-version with the 2.7 GHz i7 anyway. 
Darn it, $2500 for a 13" laptop in 2018. I’m such a sucker. 
Actually, I’m just shocked that the MacBook Air and the MacBook Pro haven’t yet been merged into a single product.
When the MacBook Air first came out, it seemed lto me It was an experimental piece of equipment to show the future direction of the MacBook Pro. The Air was a sculptured single piece of aluminum. It had no optical drive which made it over a pound lighter than the Pro. It used SSDs rather than a mechanical drive.
Yet, here we are a decade later and now confused. In that single slot of that 2x2 matrix Steve Jobs once drew sits three different models available in five different configurations. We have two MBAs, two Pros, and a plain MacBook.
The original MBA was a machine so small, it could fit in a manilla envelope. It was light, used SSDs and had no optical drive. The MacBook Pro now has all of these attributes. Why do we still need an MBA and the Pro?
I’d argue the current MBA is basically the iBook in Steve’s matrix. You need something less expensive and more rugged (Steve’s era) or more portable (today) than the MBP.
The biggest constraint of the new Macbook Air is the SSD, which has only 128 GB in the base configuration. If you get the model with 256 GB, you pay $ 1.399, $100 more than for the Macbook which has 256 GB in the base configuration. So in the end the Macbook is cheaper then the new Macbook Air if you are not willing to live with only 128 GB of storage.