The only advantages the Signature Edition have over the standard Paperwhite are:
- Wireless charging
- Bigger storage space (32GB instead of 16GB)
- Automatic light adjustment
Also I believe the standard Paperwhite can come either with or without ads, but the Signature Edition is always ad-free.
Otherwise the two devices are functionally identical, i.e. the standard Paperwhite will be just as snappy as the Signature Edition, and user the interface is exactly the same.