These sit in different price classes - Klipsch The Fives costs roughly 1.6x what Klipsch R-51PM does. Expect it to lead on paper; the question is whether the gap is audible enough in your room to be worth it.
| Area | Better | Why |
|---|
| Bass | A | Klipsch The Fives digs deeper - 50Hz against 68Hz. |
| Built-in power | A | Klipsch The Fives has the bigger amplifier (160W vs 120W RMS). |
| Connections | A | Klipsch The Fives adds HDMI. |
| Size | depends | Similar cabinet size - neither is easier to fit. |
| Expandability | depends | Klipsch The Fives: a sub output; Klipsch R-51PM: a sub output. |
| Price | B | Klipsch R-51PM is cheaper - $599 against $969, about 38% less; arguably a different class. |
A Klipsch The Fives B Klipsch R-51PM
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both speakers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
The usual trade-off: Klipsch The Fives measures better, Klipsch R-51PM costs about about 62% more% less. Whether that gap is worth the money is the call only you can make - and in a normal room it is often smaller than the numbers suggest. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 68Hz anyway, which makes the cheaper Klipsch R-51PM much easier to justify. Think about the whole system, not just the speakers: the roughly $370 saved by taking the cheaper pair would buy a subwoofer or a better amplifier, and either usually does more for the sound than the difference between these two.
And remember what a spec sheet cannot show: how each looks in your room and whether the finish suits it, what dealer support and warranty are like where you live, and how they actually sound to you. If you can hear them first - ideally with your own music - that will tell you more than any number above.