I am fixing to order a 16x36 Grecian pool and the standard pump and filter it comes with is a 1hp hayward. I am looking at upgrading to a 1.5hp 2speed Hayward for $195 upgrade charge. Would that be a good fit for this size pool? To big or small? Is 2 speed worth the upgrade charge? Also the standard filter is a Hayward pro series s244t sand filter. I am really wanting a cartridge but really do not know a whole lot about them. What size would I need for this type of pool? Right at 20K gallons. Also it will be used with a SWG if that matters