Also, by partitioning a drive, you are not doing yourself any favors. Sure the drive shows up as 2 drive letters... but it is still the same physical disk, so it will still be confined to the same max write speed as if it was un-partitioned.
Well, that's exactly what I meant when saying "we'll run into maximum disk write speed limit pretty quickly", since the maximum write speed is for the whole drive, so when writing to multiple partitions simultaneously, you'll be limited by 'max_write_speed/number_of_partitions' at best. The more partitions you write at once, the bigger penalty you'll have. If we assume the average max write speed of around 100-150 MB/sec, then it'll be 50-75 MB/sec at most when writing to 2 partitions simultaneously. I'm using 7970 cards right now, and getting 15-16 k per minute, that's what, 60-65 MB/sec.. It might actually make sense to divide each drive in 2 partitions and use 1 GPU per partition simultaneously. Would be 1.5-2x times faster to fill one drive with 2 partitions and 2 gpus, rather than to use 1 gpu for plotting on 1 big partition.