I have used quite a few different external pumps. My experiences with the CS T4 pumps have been very good. However, as you mentioned, they are not thermo-isolated from the water flow and as a result increase the tank temperature by a few degrees when the ambient temperature is about 70 deg. F.
They are extrordinarily quiet. Only 30db of sound and you have to put your ear about 6 inches from the pump before you hear anything - this is really pretty incredible.
I have also used the Ampmaster - this is a close second in terms of quietness but has the added advantage of being Termo-isolated. For all intents and purposes these pumps will not have a temperature affect on your water. They also are probably the most effecient pumps I have come across (about 100 watts for 3000 gph
flow). The big drawback - you must use 1.5" plumbing. If you are using 1 inch plumbing the flow rate is cut in half.
Also - you may want to check the BlueLine HD
seriese - these are also supposed to be pretty quiet, but still, I don't think anything will beat the CS T4 in this respect.