I've tried this:

echo 4 > /sys/block/mmcblk0/queue/nr_requests
echo 200 > /proc/sys/vm/vfs_cache_pressure

from ur setting and it seems to me an improvment.

before i did this:

echo 4000 > /sys/block/mmcblk0/queue/nr_requests.

But I have this

echo 1250 > /proc/sys/vm/dirty_writeback_centisecs
echo 1250 > /proc/sys/vm/dirty_expire_centisecs

and

usr/bin/read-ahead /dev/mmcblk0p1 4000

and also i enabled

echo 1 > /proc/sys/kernel/sched_compat_yield

which i found a huge improvement.

I have compiled read-ahead myself. what do u think? did u tried my tools? did u ran bonnie++ before and after ur optimization? i did but i forgot the result. Anyway thank u for sharing i got a hard time with this device!