I've had the occasion to run my T&D program against the Wellplan of Landmark. The ran case was a near vertical hole with two different fluid weights inside the drillstring and in annulus for simplicity reasons. However if you have access to Wellplan, you can run your own comparison with a more complicated trajectory and circulating system. The results of my program are:

The output of Wellplan was:

The differences between the estimated forces are negijable, being smaller than 0.6% or 1,400 lbf. For torque instead the differences are in the range of 7% mainly due to the different way of calculating the length of the arm of the force. The difference in the torque values implies difference in the number of the turns of the drillstring (windup) which are still neglijable in real terms. The differences in stretch are quite big and a calculation by hand suggests Wellplan has a bug here. However I will do further checks on this.


However there is logical bug in Wellplan. Let's have a look at the sliding case:

When sliding the motor creates a reactive torque equal to the bit torque but of contrary direction (i.e. turning the drillstring to the left). This torque is not seen at surface as it is counteracted by the torsional stiffness of the pipe body - just check your mudlog records for an interval drilled by sliding.
However Wellplan shows a straight line from bottom to surface with the value of the bit torque (the thick red line in the following chart):

Because of this, the torsional stress while sliding is also a straight line from bit to surface:

The rest of the data match pretty well:

Fell free to download the output data file in case you would like to see the matching for all the cases.