A lot of this will depend not only so much on the gallonage of the pool but also the bather load. A home pool @ 50,000 gallons with a family of 4 using it several times a week is a lot different than a 50,000 gallon public or commercial pool with 75, 100, 200 bathers per day. If you want to cut down on the back washing of your sand tanks and save water, chemicals, etc. you may want to consider looking the MultiCyclone from Waterco (disclaimer: I'm a distributor for Waterco). It has been third party tested to cut down on backwashing quite a bit. There is a small past thread on TFP about it: waterco-multicyclone-centrifugal-filter-t28631.html
Ok, I am going to buck the trend here a little. A 525-sqft cartridge filter for a 50k pool exceeds NSF/ANSI 50 minimum requirements by 40%. So unless the pool gets really dirty really fast, you probably will be able to get away with once a year cleaning or at most twice a year cleaning. Add to that the Salt and CYA issue, I think it might not be a bad decision.
Also, I clean my filter once a year and it really isn't that bad. I can usually clean each of the four filters in 10 minutes so less than an hour total.