VideoCardz heard rumors that AMD is working on a new line of mainstream GPUs codenamed Tonga. The chip will likely be made on a 28nm process by GlobalFoundries and it will probably be a direct competitor to NVIDIA's Maxwell GM107.
Tonga is said to be a redesigned GCN core with enhanced power efficiency. If the rumors are right, Tonga will deliver a "dramatic change" in power consumption. It will also introduce PowerTune Boost, which would operate at a much lower hardware level.
The first Tonga-based cards are anticipated about two to three months from now.
Graphics card based on Tonga should be released in about two to three months. The sad news is that Tonga-powered graphics card will only feature 2GB memory (at least the reference model). This basically means we have a new Pitcairn (Curacao) replacement.
Probably the the most suitable name for this card would be R9 275X, but from what we’ve learned, final codename has not yet been decided.