According to pictures posted by Videocardz.com, which show engineering samples of the Radeon RX 570 and Radeon RX 580, these cards are rebrands but with a slight change in the power department, which suggest that these will indeed come with a higher clock.
The Radeon RX 570 will use exactly the same PCB as the earlier available Radeon RX 480/470 series graphics cards and still be powered by a single 6-pin PCIe power connector. There is no need for higher power as it will still have plenty to reach the rumored 1244MHz GPU Boost clock and come with 4GB/8GB of GDDR5 memory clocked at 7000MHz.
The pictured Radeon RX 580 is a bit of a different story as the reference design uses the C940 PCB which has not been seen so far. This new design implements an 8-pin PCIe power connector, suggesting that the RX 580 has a higher power consumption which is in line with previous rumors that it will be coming with a much higher 1340MHz GPU Boost clock.
Both the RX 570 and RX 580 should be using the same Polaris 10 GPU with 2304 Stream Processors, 144 TMUs and 32 ROPs and stick to standard 4GB/8GB GDDR5 memory, clocked at up to 8000MHz, on a 256-bit memory interface.
As you probably already know, Nvidia is using a higher clocked memory on its GTX 1060 and GTX 1080 graphics cards but due to a narrower memory interface, the Radeon RX 570 should have a higher total memory bandwidth (224Gbps over 216Gbps).
Earlier rumors suggest that the rebranded AMD Radeon RX 500 series will launch on April 18th, about the same time when Nvidia is expected to launch its memory-updated Geforce GTX 1080 and GTX 1060 graphics cards.