I only have experience with the d5 vario, I picked mine up on the MM for £35 and it's been a great buy. I use it on speed 2 and it's inaudible to me, i used the higher settings when bleeding. Only down side is it has pre moulded 1/2 barbs although you can get after market tops that have standand g1/4 threads.
As already said tubing bore makes no discernable difference to temperatures.