One thing to consider is the dimensions of the two pumps. The Northstar has a higher inlet port and the outlet port is set back farther. It also as 2" ports instead of 1 1/2".
There are also two 1 hp versions of the Northstar. An max rated one which is really the 3/4 hp one, and a full rated 1 hp. The flow rates are different. From the performance data listed at the Hayward website for the 2 pumps, the full rated 3/4 hp or max rated 1 hp Northstar come closest to the 1 1/2 hp Super Pump in performance and still has a bit more flow.
Of course this is assuming that the current pump is the correct size. See http://poolplaza.com/pool-pump-sizing-2.shtml for an idea of what is involved in determining the pump size. There is a posting in the forum here somewhere that has some good info on pump sizing and another link to a page for figuring out pump size.
As an example I have a 2 speed 1 hp Super Pump on a 20,000 gallon ig pool with the pump and filter 15' from the pool edge. I get enough flow on high to over power a Polaris 360 and I have 2 skimmers and returns. So feet of head is everything.
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