VideoCardz explains there's still some uncertainty about the naming of this chip, most believe it will be R7 series though but a newly leaked screenshot suggests it could end up as R9 370 series.
If the leak is accurate, the 370X is based on a full Pitcairn GPU. As you may still remember, Pitcairn (GCN 1.0) was first introduced in 2012 as the Radeon HD 7800 series and has since served as the base of various GPUs, the latest one being the Radeon R9 270X.
The 370X reportedly has the full 1280 stream processors of Pitcairn, 80 TMUs, 32 ROPS, 2GB GDDR5 memory, a 256-bit memory bus and clockspeeds similar to the R9 270X. So yeah, in the end this card looks pretty much identical to the R9 270X.