I will relate the level of SFE to climb of dislocations in a qualitative way. Climb is always possible however, if we compare different cases with different level of SFE, as SFE gets lower the stress field around a dislocation increases (core size of dislocations gets larger) and therefore climb motion is facilitated. The reason is as follows: Every dislocation have quite a complicated stress distribution around them but in a simplified version we can safely say a dislocation (please consider the representation of a dislocation with an upside down capital letter of T as seen the figure attached) has a compressive stress field at the upper portion and a tensile stress field below. One has to remember that the compressibility of atoms are extremely small. This means atoms, if they have the thermal activity, i.e. capability for diffusion, to move they would move out of regions under compressive stress fields. In the case of the atoms around a dislocation the atoms that are sitting on the dislocation line, which is within the compressive stress field of the dislocation, would move out of their positions, especially with the help of vacancies, into the region of tensile stress field as this is the only neighebouring region. This movement is named "climb" and it happens during creep (the number of vacancies become sufficient at creep temperatures). And because the stress around a dislocation increases as SFE is lowered (core size of dislocation increases) the climb motion is facilitated.

This explanation holds well for a pure system and for the host atoms sitting on the dislocation line in a solute solution. However, the solute atoms do require further evaluation as their size is different compared to the host atoms. When considering the solute atoms sitting on the dislocation line the stress field around this dislocation becomes very complicated. The solute atoms depending on their size difference with the host atoms may cause relaxations in the compressive stress field around the dislocation or do otherwise. In other words the level of the compressive stresses may change locally. This determines whose diffusion (the host atoms or the solute atoms) would control climb. Thus the climb motion (in other words the creep rate) becomes dependent on the diffusion of the host atom or the solute (alloying element). This argument can further be evaluated as the changing core size of the dislocation with changing SFE also provides a diffusion path.

Regards