How much more storage than iOS 7 does iOS 8 ACTUALLY use up?

I have read so many reports about iOS 8 installation storage requirements that I've lost count, and none of them even answer this very basic question.

“The download is 1.2 Gb… the free space requirement for the install is 5 Gb…” etc... But honestly, who cares? We get the space back after it’s done. It's a one time requirement.

What's ultimately of interest when I install iOS 8 on my iPhone 5 is: how much space will I never get back?

The Ars Technica iOS 8 Thoroughly Reviewed article pegs it at 600MB difference on the iPhone 5.

DEVICE  SPACE AVAILABLE    (IOS 7.1.2)  SPACE AVAILABLE (IOS 8.0 GM)
32GB    iPhone 4S (AT&T)    27.4GB      26.6GB
32GB    iPhone 5 (VZW)      27.3GB      26.7GB
32GB    iPhone 5C (AT&T)    27.2GB      26.5GB
64GB    iPhone 5S (AT&T)    56.0GB      55.1GB

When you complete the upgrade to iOS 8 on the iPhone 5 - you will have 27.35 GB of usable capacity out of 32 GB of "marketing" storage. If your phone is smaller or larger than 32 GB, approximately 4.6 GB will be reserved for overhead.

On iOS 7 - you probably lost 4.1 GB, so the loss would be 500 MB on the upgrade from 7 to 8 for a 32 GB device.

For past OS see:

• How large is iOS?
• iOS 7 upgrade - how much space will I get back?