To reduce memory usage and improve performance we did some tests with sequential mode read, from our tests in looks promising. However we're missing 1 function that is in libvips and not in the PHP binding:

• vips_get_tile_size (some operations needs a tilecache to prevent over-computation)

General question:
Sequential read mode does not work with rotate, sharpen, gaussblur and our trim function. If we have to deal with these operations we force the access mode to VIPS_ACCESS_RANDOM, do you recommend this? I was not sure if a tilecache fixes this.