With obvious complaints of my machine, I managed to squeeze out a crop of a total sized render of 28000 x 6222. 98% of memory was used, 15.8 GB. Subdiv cache at 800. Detail 0.4, AA4 again, this time GISD worked ok. So I guess it's the size that takes up all this memory anyway. Oshyan; maybe you didn't read the resolution properly, it's not 3240, but 32,400! If that's still strange, there must be something else wrong. Assets are very scarce.