what hashrate can R9 370x give on zcash using claymore?
Not -quite- the same card, but I have one I believe is at least kind of one of those, as it's an R7 370 with a Pitcairn XT instead of a plain'ol Pitcairn core.
XFX R7 370 "redline series", detected by miners as either "Pitcairn XT" or "R9 270/270X", with 20 compute units. It has 2GB of Samsung memory on it, default memory clock is 1400. It's stable at 1500mhz mem clocks and 1125 core and gets around 210 SOL/s there, I forget what it got with stock core clock, but the memory on stock at least it was getting around 180 SOL/s.
edit: It was stable but got worse performance through most of the OC'ing past 1400 until nearing 1500.