Something

livecd ~ # dd if=/dev/sdb of=/dev/null bs=16384 count=64k
65536+0 records in
65536+0 records out
1073741824 bytes (1.1 GB) copied, 13.9409 s, 77.0 MB/s
livecd ~ # dd if=/dev/sdb of=/dev/null bs=8192 count=128k
131072+0 records in
131072+0 records out
1073741824 bytes (1.1 GB) copied, 13.9103 s, 77.2 MB/s
livecd ~ # dd if=/dev/sdb of=/dev/null bs=4096 count=256k
262144+0 records in
262144+0 records out
1073741824 bytes (1.1 GB) copied, 14.1214 s, 76.0 MB/s
livecd ~ # dd if=/dev/sdb of=/dev/null bs=2048 count=512k
524288+0 records in
524288+0 records out
1073741824 bytes (1.1 GB) copied, 14.5994 s, 73.5 MB/s
livecd ~ # dd if=/dev/sdb of=/dev/null bs=1024 count=1024k
1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB) copied, 15.4477 s, 69.5 MB/s
livecd ~ # dd if=/dev/sdb of=/dev/null bs=512 count=2048k
2097152+0 records in
2097152+0 records out
1073741824 bytes (1.1 GB) copied, 16.9333 s, 63.4 MB/s
livecd ~ # dd if=/dev/sdb of=/dev/null bs=256 count=4096k
4194304+0 records in
4194304+0 records out
1073741824 bytes (1.1 GB) copied, 19.8017 s, 54.2 MB/s