Curious.  On what basis do you make this statement?  "Should be way less.  Like a lot less."  Given what I know, 4% seems like a pretty good deal.

Probably not.  You get 20x performance improvement on the DDR4<->FPGA interface but no improvement anywhere else.  So the algorithm you are accelerating must require high amounts of sequential access to a large memory bank.  And any algorithm could be made resistant to acceleration by an HMB/FPGA merely by requiring >16GB of memory.

... And the present price of the HBM devices is *shocking* ...  Better from Intel/Altera than Xilinx, but still more than this market can tolerate.  Also, Intel/Altera has not executed well in the last 2-3 years.  Getting a Stratix10 device has been a bit of a joke in the FPGA world.

Your '500' is very low.  5000, and possibly more, of the 1525 variants will enter some sort of operation within the next few weeks.  This is gonna be a race until the rigs become unprofitable. 

I would add that the secondary market for these boards, once rendered unprofitable for altcoin mining, is nil.

PS -- The '300A' Bittware card is a single FPGA?  VU13P maybe?  Seems like overkill.

Hey -- Management appears to restrict experts from chiming in.  But I would comment that the thread 'Modular FPGA Miner Hardware Design Development' is VERY amusing ....

Nope.  You can get them from Digikey for $152:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=XC6SLX150-2FG484C-ND

The LX150T for $172:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=XC6SLX150T-2FGG484C-ND

mike_la_jolla checking in here to clarify some FPGA questions.

- DNDPB_S327:  http://www.dinigroup.com/new/DNDPB_S327.html
List price is $19,680 for quantity 1.

- This is probably a much better choice:  DNBFC_S12_PCIe: http://www.dinigroup.com/new/DNBFC_S12_PCIe.html
List price for quantity 1 is $8,950.  We sell thousands of these to do (spooky) things.  We can fit 12 in a single chassis.

- 300 MHz is probably not achievable for Spartan-6 or Cyclone 3.  With some effort by an expert, assume you can get to 200 Mhz or so.  Don't bother with the 'C' to FPGA methodologies.  You'll need someone that is well versed in VHDL/verilog.  Also, you generally can't get to 100% utilization without breaking the tools.

- Any FPGA solution will required a host.  The DNDPB_S327 connects via Ethernet, so has low data throughput.  The DNBFC_S12_PCIe is GEN1/GEN2 PCIe, so the bandwidth is much higher.

- Those of you that think you can do a custom ASIC are nuts.  The expense and effort of an ASIC would cost millions ($USD).  The Genomic search market isn't even large enough to support a custom ASIC.

- If this is a pure code breaking application, you are probably better off with FPGAs than GPUs, but it is very easy to gang together a few Xboxes.  FPGAs are harder to come by.