The math is a fairly accurate estimate, but each system varies a bit because of motherboards, drivers, voodoo/kami, etc.
On my 560s (4gig) I use 508, w4, g2. - 450h/s (on another board, 480 was the magic number)
On my 570s (4gig) I use 896 w8, g2. - 840h/s
All are bios modded, and moderately overlcocked at 1860-1880.
Heh, those are exactly the numbers I have programmed for my RX 570... Too bad the miner crashes so soon after startup, and doesn't even leave a debug log despite setting...
Wait, I got it running after I removed the switch "--shaders 2048" from the command line (forgot I had that) and changed the debug switch from "-D" to "--debug-log", which really shouldn't have affected anything. Unfortunately, the bad news is that the hashrate is terrible - about 90 h/s so far. But, I can work with a bad hashrate; I can't work with an instant-crashing program.
EDIT - Oh, I forgot I also changed "gpu-platform" in the config file from 1 to 0; I suspect that is what solved the problem - as I think I read somewhere else, 1 is for systems with an integrated GPU on the CPU.