AMD launched some new FirePro workstation cards based, including the W7100, which is based on the Tonga GPU. This new chip will soon be used for The Radeon R9 285 lineup so the W7100 gives a basic idea of what to expect. The W7100 has 4 compute units (CUs) disabled so the full version of Tonga may offer up to 2048 stream processors spread across 32 CUs although it's believed that the Radeon R9 285 will be limited to 1792. A future R9 285X however may unlock the full potential of Tonga.
Tonga is based on GCN 1.1 architecture, it has increased primitive rate and larger L2 cache. Tonga has TrueAudio and XDMA CrossFire support.