I did some GPU testing with high N values. The gist is: at N=8192, I couldn't get it to output valid shares any more. Therefore, with current information, it seems that GPU mining will stop on 13 Aug 2013 - 07:43:28 GMT when N goes to 8192.
Very interesting news. Might there be some additional optimizations that you could do to get it to output (perhaps like messing with the lookup gap or some other TMTO hacks?)
I'm wondering two things:
a) why do you think it stopped working at 8192 (physical GPU limitation with current gen GPUs, or more a limitation of the code that can be more easily overcome)?
b) does CPU mining still work at 8192 and beyond? (if not, then we have a problem on our hand that would at minimum necessitate a hard fork I'd think).
Thanks for your insightful work on the GPU miner around YAC.