Can someone explain how to read specs of a FPGA? I know to read and compare GPU specs and tell what is "good", "fast", "if this is high, its good for mining this or that"...
FPGAs are not GPUs.At all. They are completely different. Every board design requires essentially its own miner to be specially created for it. You basically need to get one of the ones the community is focused around or have the resources to develop your own. Every miner will run at some unique clock speed and power envelope. The FPGA does not have a native clock speed.
With that said, specs are usually on the AC & DC Switching Characteristics datasheets. Generally useful comparison points are the number of LUTs, or sometimes easier the number of Logic Elements, amount of Block Ram, amount of Distributed Ram, amount of Ultraram (keep in mind all memory sizes are usually specified in bits, not bytes, so divide by 8 to get numbers you’re used to), speed rating, temperature rating, family (Kintex vs Virtex), process (45nm, 28nm, 16nm - usually results in higher maximum clock speed or lower power). What hardblocks(PCIe, memory controllers, DSPs) are included, maximum power capacity. Mounting size.
In short it is very complicated and the selection of a specific chip for a new board or project is a whole project in and of itself.
I have been burned twice by ASIC's, no more.... 
