Load depends on how you wire them (parallel, series, channel) and/or whether you want them in mono or stereo.
They have some decent generic info here:
http://www.crutchfieldadvisor.com/le...8NI9w5KrD/car/
I'd say if you're looking to put that much through them you'd probably be better off with one amp per sub.
There's a few folks here pushing that many watts and if memory serves most (if not all) of them ran dual amps for their subs. But they should be able to give you more detailed info.