To get the full radio rates of the ac product, you need a clear 80MHz channel. Assuming you are installing in the US, you might find that difficult given the small amount of spectrum you currently have available. So in practice you may be limited to 60 or 40 MHz. Nevertheless even at 40MHz you should be able to reach sustained user rates well in excess of 100 Mbps. So you are probably right to go with the flexibility offered by the Powerbeam. The larger dishes will also provide more directivity and hence greater isolation from external interference.