In Patch 2.3, speed boost was increased to 8/15% from 4/8%.
This stacks with the Subtlety talent Camouflage. Contrary to its description, Camouflage actually reduces the speed penalty of being Stealthed, rather than giving a boost in speed. With maxed ranks in both talents, your speed while Stealthed is reduced to 97.5%.
Many raiders skip this talent despite that it actually is a DPS increase. The less time you spend running away from fire, poison, oozes or other unhealthy stuff, the more time you spend attacking the boss.