Break a pat straight for 4 to a royal?
Yes, always. Exact EVs on 9/6 Jacks or Better: the K-Q-J-10 royal draw is worth 19.5957 per coin vs 4.0000 for keeping the made straight — nearly five times as much.
The exact numbers — K♠ Q♠ J♠ 10♠ 9♦
EVs are exact — every possible draw enumerated, not simulated — at max bet on 9/6 Jacks or Better. Check it yourself: the analyzer runs the same solver in your browser.
See all 32 holds of this hand ranked →Why
One of the 47 remaining cards is the A♠ that completes an 800-coin royal, one more remakes the straight flush, and even the misses often land straights, flushes, or high pairs. This draw is worth more than a made FLUSH (6.0) — it's the strongest non-made holding in the game, which is why it outranks every pat hand below a straight flush.
Chart line #2 of 18 — 4 to a royal outranks any made straight or flush. Same logic as breaking a flush, with an even bigger margin. See the full solver-optimized strategy chart, or drill hands with exact-EV feedback until plays like this are automatic.