Attached PDFs show graphs of vmstat -n 1 recorded 'bi' and 'bo' data for the same test using different io schedulers under a fresh install of CentOS 5 with the built-in 3w-9xxx driver.
The test was:
dd if=/dev/sda of=/dev/null bs=1M count=4096 &; sleep 5; dd if=/dev/zero of=./4G bs=1M count=4096 &
Twin Opteron 2.4GHz, 4GB RAM, 3ware 9550SX RAID 1, built-in driver 2.26.02.007, nr_requests 128 (default), ext3 on LVM (default), data=default (as opposed to 'writeback' or other non-default tweaks). All other filesystem/kernel param settings also at default for the CentOS 5 install - only the io scheduler is being changed.
Also tested the 3ware 126.96.36.199 src-compiled driver and saw identical results.
Edit: Redid tests with 4k blocksize and count 1048576 - very similar graphs.