I'm going to be replacing my HiFonics BXi1606 with one of these amps...I currently have 0/1 guage running from the battery to a fused distro block that has (4) 4ga outputs...the length of the wire running from the fused distro block to the amp is about 12 inches...would it be okay to run 12 inches of 4ga to the power input of this amp?

That is fine.

I figured it was...was just checking to make sure.

Any idea what kind of RMS that amp will do @ 1ohm seeing a 14.2 voltage?

My personal testing has shown with a solid electrical using 1/0 connections you can top the 2kw mark, i would expect you would be somewhere in that neighborhood. But every install is different, at the very least I would expect 1700 watts

I have pretty good connections...have a 260amp alternator (175amps @ idle)...a Red Top (needed the cranking amps as I don't sit and listen to it with the truck off)...big 3 done with 1/0ga...and 1/0ga running to a distro block in the back...will only be about 12" of 4ga to the amp from that...1700rms would be plenty for me...any more would simply be icing on the cake.