The Hayward filter is bigger.
I asked Pentiar about this, they replied "for a self install the warranty would only be 60 days parts only"
The 3 item deal doesn't apply for DIY builds.
Your doing the install, meaning your doing the plumbing, and electrical hookup yourself?. I would assume it would be a pool plumber, and electrician, who are a licensed professional. So no "self install".
Then you fill out and follow directions on this.
http://www.pentairpool.com/pdfs/LimitedWarrantyCard.pdf
As far as size goes, I have a 520 on my 65,000 gallon pool, with no issues. Cartridges are 10 years old, and still look new.