freebsd 7 current
1:    read/write requests:                 650000 (1052.57 per sec.)
2:    read/write requests:                 650000 (1484.22 per sec.)
4:    read/write requests:                 650000 (1658.24 per sec.)
8:    read/write requests:                 650000 (1625.35 per sec.)
16:    read/write requests:                 650000 (1147.05 per sec.)
32:    read/write requests:                 650013 (721.33 per sec.)
(i stopped it here, because performance was dropping)

linux-2.6.25-rc4-git2
1:    read/write requests:                 650000 (1385.70 per sec.)
2:    read/write requests:                 650000 (2344.83 per sec.)
4:    read/write requests:                 650000 (3616.27 per sec.)
8:    read/write requests:                 650000 (4129.50 per sec.)
16:    read/write requests:                 650000 (4691.78 per sec.)
32:    read/write requests:                 650013 (6016.29 per sec.)
48:    read/write requests:                 650013 (6456.23 per sec.)
96:    read/write requests:                 650026 (6969.38 per sec.)
128:    read/write requests:                 650013 (7047.83 per sec.)
192:    read/write requests:                 650000 (7038.01 per sec.)