I have the 860watt version of this PSU in my computer, it's "probably the best psu ever" according to anandtech:
http://www.anandtech.com/show/5464/seasonic-platinum-series-860wSince I need to have my computer on to mine I will use the computers power supply to power the bASIC's of course, but I would need really long molex power cables (want to have boards around 1.5meter from computer), any ideas where they sell meter long of those or I need to make them myself?
I don't know that (you could really easly do that yourself, just be sure you take great cables).
A sidenote: tension decreases with the distances of the wire. So if you have a 10 meter long wire and you start at 12V, you might arrive at 11V at the other side. I would be sure that i did it right before risking to damage Xk$ of mining device.
finding one will be a miracle, it is intended to be an internal connector. You should be able to get the connectors pretty easily since they have been standard in industrial and computer equipment for 40+ years.
Tension=voltage?
Resistance increases as you go to a smaller wire (higher gauge) as well, so be sure to keep those lines nice and fat since they will be carrying 100W DC.
100W at 12V makes for a load current of 8.333A.
If you use 18 AWG copper wire, on a 1 meter run, you would see a resistive loss of about 0.349V from the wire (that counts the loss from both the positive and negative wires, 2 meters of wire total to make a complete circuit). A 2 meter run would be double the loss, etc.
The connectors may also introduce some loss.
Edit: If you're using 4-pin molex, and both of the negative wires are connected at both ends, the loss from the negative side would be cut in half, from using 2 wires instead of 1. So 0.262V for a 1 meter run.
I base my numbers on this data:
http://www.powerstream.com/Wire_Size.htmI would hope the bASIC units have nice on-board regulators that can deal with a bit of variation in the input voltage.