I have a 325 gal Fish Only tank. 40" stand and 36" tall tank. I want at least 2400 GPH at 7". The tank is plumbed for a 1" inlet from the sump and 1" return into the tank. I'm running a Coralife Turbo-Sea 1740-P for return. This pump is extremely loud and inefficient with a lot of heat transfer. I can't get the tank below 81 degrees!  

1.) Need QUIET, EFFICIENT, LOW WATT, NO HEAT TRANSFER, Hi GPH pump that can run 1" in/out. I'm leaning toward the Dart or the Dolphin 3200. 

2.) Ideally I don't want to have to redrill my sump and tank to 2" / 1.5" inlet/outlet to accomodate the new pump.

Do I need to replumb?

Is there any way to get either the Dart/Dolphin and run 1"/1" without harming the pump?

If not, can I split the return bac into the tank to 2 1" lines?

I am assuming you mean 7 feet, not 7 inches correct?  

I have one of the older Dolphin Amp masters and they are silent and have no heat transfer that I have noticed (although I am sure there is none that have a zero transfer, this one is pretty close).  If the newer models are along the same lines it may be the way to go.  I also have a Sequence 3200SW pump.  It does run a little louder than the Dolphin, but still fairly quiet.  I had a Hammerhead before that and it did transfer more heat than the SW series pump does and was a little louder (also it was a more powerful pump).

I would not decrease the input into the pump as this can cause cavitation (microbubbles and such).  You will want to keep this the same size plumbing coming in.  I did talk with one of the reps from Sequence and he did say dropping it down 1/2" (from 2" to 1.5" was ok, but would be much better to stay at the same size).

With the older dolphin pumps they use to estimate that decreasing the output tubing (from 1.5" to 1") would decrease the flow by 25%.  I am not sure if that still hold true, but I would assume it is pretty close to that.

I don't think either of the two pumps you listed will acheive the flow rate you are looking for, especially if decreased to 1" inlet/outlet

Unfortunately this may need to be done to have these pumps work properly.  If they have to work harder to pull water into them, it may cause more transfer of heat, louder operation and cavitation of the pump.

If you want to go with one of the Sequence or Dolphin pumps, I would recommend doing this.

You may want to contact the manufacturers directly to double check, but I think it will harm the pumps over time. http://www.dolphinpumps.com/ and http://www.mdminc.com/Sequence_Pumps.htm or http://www.reeflopumps.com/