You can have multiple Chase Freedom cards and up to two Discover It cards.
For Chase Freedom(s), this is assuming you value your Ultimate Reward (UR) points at 1 cents per point (CPP). If you have a card like the Chase Sapphire Reserve, you can book via the portal at 1.5 CPP or transfer them out to partner programs for 2 CPP or more (i.e., 3.6 CPP in our recent “free trip to Hawaii” post). This means that 5x is really 7.5% to 10% (or 18% from our trip example).
For Discover It, you can effectively always be in the first year for one of the two cards (get card #1 and keep it forever, get card #2 for a year and replace it with card #3, etc.). When you’re in your first year, any cash back you earn is doubled via their “cash back match” program. This means that 5% is really 10%.