I've been using 16,384 for 64GB SD cards with guiformat (the default is twice as large). I noticed problems with slow log file writes on the G1X while saving pictures with a 64GB card that didn't happen with the 32GB card. It seems to have helped.
16,384 is the default for the 32GB card with guiformat.
You might try formatting at different sizes and measuring boot speed and read/write speed to see what the difference is. That's what the "H" stands for.
Also, where did you find the benchmark program on the camera? Thanks.