IMO - there are too many clicks and too many pages in the checkout sequence.
Amazon's concept of "One Click Checkout" is now an old concept. They made it for a reason. Customers want to be done.
This is what my customers see:
Cart - GS1 - GS2 - GS3 - Success.
Cart - paypal - GS2 - GS3 - Success.
GS2 is redundant. Move Comments to GS3. Payment selection has already been made, it does not need to be made again. Eliminate GS2.
I'm not saying that AC needs 1-click checkout, but I think it can be faster and cleaner.
I think it would be easy to eliminate GS2.