First, you can only use the powergui if you're using SimPowersystems. In fact, it is required with those blocks.
Second, the solver choice completely depends on the model. Why can't you use a variable step solver?
If you are planning on using fixed step the ODE# indicates accuracy where 5 is more accurate than 4. Once you find an ODE solver accurate enough for your simulation you can utilize accelerator or rapid accelerator mode to speed up the simulation time.
