I think people using Spartan 6 will not get any higher hashrate from now and it looks like 180 - 200 MHash/s is the cap.
Doesn't eldentyrell three ring structure improve the performance or at least it will when the clock rate improves?
https://bitcointalk.org/index.php?topic=49971.0;allmarked
Yeah the prior person likely mispoke. Some higher performance is possible. ztex has boards running at 212 MH/s. Still nobody is going to get 400 MH/s out of a Spartan so there will be no massive performance boost where a board costing roughly the same gets 25% or 33% or 50% higher performance. The Spartan-6 is pretty well analyzed how so it is in the fine tuning. A couple MH/s here and there. Maybe someone gets a board going @ 220 MH/s which would be a nice 10% "free" compared to existing bitstreams but
significantly higher performance is going to require a new class of chips.
There is no other 45nm chip which delivers the LUTs/$ that Spartan-6 does (without special "sweetheart" pricing) so that means waiting for the Artix-7 28nm chips to become available and at reasonable cost. The largest Artix-7 chips likely can (eventually with a lot of bitstream analysis) achieve 500MH/s+ so a pair could provide the first GH/s board. Still who know how long it will be (Q1-2013 ?) before Artix-7 provides better MH/$ than Spartan-6 does.
The new Artix-7 28nm chip from Xilinx is for sure one of the most interesting new FPGA for mining. Unfortunatley this chip is not yet available, and what is even more worse there is no official announcement when it will get available. When the production of this chip starts it could also take a longer time until the chips are really available on the market for attractive costs, because large companies with high volume are already waiting for this type of chip to assemble their boards.
This week is the Embedded World tradeshow 2012. Maybe I can get some more information about the availability at the trade-show, but I guess we have to wait at least 6 month until a 28nm FPGA miner will be available. Spartan-6 is already available now and you can use the time (with a 50BTC blockreward) until the end of this year to compensate your investment in FPGA. I guess 28nm FPGA miner will start in the time area of 25BTC blockreward. So it will take much longer until you have your return of investment. Beside all of this the 'risk' grows that someday, someone announce a SASIC or even an ASIC.