Sorry, off topic too.
X6500: $580 / 250MH/s = $2.32/MH (with early payment discount, it's $2.24/MH)
ZTEX: $460 / 190 MH/s = $2.42/MH
You forgot to mention that there are volume discounts, see
https://bitcointalk.org/index.php?topic=49180.0, e.g.:
5 x UFM-1.15x: $2100 / 950 MH/s =
$2.21/MH10 x UFM-1.15x: $3900 / 1900 MH/s =
$2.05/MH25 x UFM-1.15x: $9000 / 4750 MH/s =
$1.89/MH...