I have both a 640 Pro, and a 340PD.

For belt or ankle holster carry the 640 is much preferred. It is easier to shoot, and the weight does not bother me at all on the belt or the ankle.

For pocket carry the 340 is preferred. The stainless steel 640 is just too heavy for comfortable carry in the pocket.

On the range I practice with 38s on the 640, and then fire 5 rounds in .357 to finish off.

I fire just 5 or 10 rounds of .38 out of the 340PD on the range. larger quantities leave nerve bruises that take time to recover.

I carry 4 rounds of .38 in the 340 with the last round in .357.

I rarely carry the 340 as I wear a jacket or untucked shirt to cover my S & W 686 on the belt, and my 640 on the ankle.