The Kintex and Virtex FPGAs are basically the same. The Virtex just comes in bigger sizes and allows for higher speed serial transceivers (up to 28 Gb/s).
As a reference, I've been using ML605s at 375 MH/s since 2011. That's just using 3 copies of the verilog port, with some of the adders replaced by DSPs (Not pipelined). It's also using some space because I use PCIe for the connectivity to the PC. So, you could use 375 MH/s as the benchmark for your ML605.
It's possible that there is more speed in there using more pipeline stages, but the size of the device limits what can be done. I haven't tried to get more out of it so far.
I've been trying to get 300+ MH/s out of V6LX130Ts, but only have it running at 200 Mhz right now (using PCIe as the connectivity method again). I've been trying to fully pipeline the DSPs (as FPGAminer has done with the KC707), but the problem is there aren't enough registers/dmem to delay the rest of the pipeline in that device (plus it does not have enough DSP48s to replace all the adders).
I just did a scan over the 7 series datasheets to see their relative performance. Here is a summary of the important figures; I figure they might be helpful for this and any other 7-series based projects:
Everything is for the -2 speed grade Artix 7 | Kintex 7 | Virtex 7
FIFO Fmax | 460.83 | 543.77 | 543.77
DSP48E1 Fmax | 550.66 | 650.20 | 650.20
The FIFO Fmax (block ram) has been a fairly good measure of the absolute maximum frequency we can expect to see out of hashing cores. My rough estimates show that Artix 7 is likely to have a better MH/s/$ based on these figures alone, and single unit prices. However, it is difficult to tell for sure, because I suspect that the Artix is crippled in some other way. I have not check each chip's routing and CLB configurations.
I'm suprised that the kintex and vortex are equal, I would expect the virtex to be quiet a bit faster xD
but thanks, for this, this means the FPGA should put out about 1GH/s