There is no programmatic 5th night free on regular paid stays.

Sometimes when you price a long-ish stay, you'll get a lower nightly rate...sometimes not. Sometimes you have to play around with it: price the weekend nights separately from the weekday nights. Many times a property will have an "Nth night free" promo code, but sometimes that simply kicks in a higher base rate than whatever other "best" code you were using.

In any case, the C&P award seems (to me, anyway) to be intended for short stays. I always thought this was a big Starwood advantage to have these awards, and when HH introduced them I was pretty happy as well. (Conrad HKG was a good place to use them and may still be, depending on their rates.) They create a usefulness for points when you aren't planning on a big AXON/GLON type stay. As much as I love Marriott Travel Packages, it's a bit restricting that MR points are so incredibly useless for 1 or 2 night stays.