The best info I could get from SanDisk's website is:

Capacity: 480 GB
Read Speed: up to 550 MB/s
Write Speed: up to 515 MB/s
Interface: SATA Revision 3.0 (6 Gb/s)

SanDisk Extreme PRO SSD Review and UserBenchmark: Samsung 850 Pro vs SanDisk Extreme provide much more detail, but the word "sustained" does not appear in either.

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire