Models of a working (short-term) memory task that combine performance and reaction time?
This is a tough question, one that I have had to face in my own research. Your question has already been answered/addressed in How to analyze reaction times and accuracy together?

In short, there is no universal method. If you don't find the references or methods listed in that question useful, then I suggest you will require a computational model such as the Linear Ballistic Accumulator. The LBA is a (structurally and computationally) framework that informs process underling both RT and error data (drift rate vs response criterion).