> did you try either 1) forcing a bitmap scan (of only one index), to force the heap reads to be ordered, if not sequential? SET enable_indexscan=off (and maybe SET enable_seqscan=off and others as needed). Disabling index scan made it bitmap. It is surprising, but this increased read speed in both ranges. It came two times for "fast" range and 3 times faster for "slow" range (for certain segments of data I checked on, the whole experiment takes a while though). But there is still a difference between the ranges, it became now ~20 MB/s vs ~6 MB/s.
Vlad
