The gaming cards do really well (only the Quadro K6000 is faster), but we have to set them aside; nobody's going to use a consumer-oriented product in the medical field.
With those out of the way, we're left with essentially the same picture painted by Energy, the other synthetic volume rendering benchmark. Not only does AMD's FirePro W7000 dominate the Quadro K5000 in yet another suite, but the FirePro W5000 manages to beat the Quadro K4000 by a good margin and is almost twice as fast as the similarly-priced Quadro K2000.
Just remember that this is a synthetic collection of tests, though. It puts an emphasis on memory capacity and performance. While representative of the workloads encountered in the medical field, SPEC's benchmark primarily provides a good summary of how these cards might fare in real-world applications.