Right. In general the 1 5/8" tubes are a little better for low end torque.
One example of headers with thicker flanges and tubes are the Hedman Elite headers. Standard Hedman headers have 1/4" flange and 18 gauges tubes, while the Elite have 3/8" flanges and 14 gauge tubes. There is nothing wrong with the standard headers, but the heavier ones will stand up better over time, especially on a truck that is driven off road.
However, you also need to consider the cost and how long you will have the truck, since the heavy duty headers are almost twice as expensive.