607
Realtek's $10 tiny 10GbE network adapter is coming to motherboards later this year
(www.tomshardware.com)
This is a most excellent place for technology news and articles.
The Realtek RTL8125B on my year-old motherboard has been doing fine with Linux's r8169 driver.
I've only used it at 1gbit/second, though; I haven't tested its 2.5gbit mode.