An eight element array is probably easily modeled in HFSS. Models that result in gain on the order of 25 dBi or less usually fit. If not all you need is more ram and HPC's to make it run faster.
Without knowing the bounds of your model it is not possible to give you more specific advice. A while ago I simulated a 1x12 linear array and corporate feed in HFSS. The particular simulation took many hours on a reasonably heavy workstation but I had a considerable amount of detail in the model.
I created a straight FEM model and did not use the array simulation features in the software.