Is there any way to power 4 of these with a single 1600W Gold/Platinum PSU, or am I just asking for a fire hazard? What PSU is everyone using for 2-4?
In my opinion it's always better to have two smaller PSUs than one big, because even if everything will work great, you still have some chance that a PSU will break, and if it does, your second PSU will be still powering two boards.
Also you should expect, that after some time a PSU that is running on full load will start to supply less power.