What is the strongest continuation for White?

Casual 5+2, Greenwood Chess Club
Coffey, John (2016) vs. Gusev, Dmitri (1865)

8 7 6 5 4 3 2 1 a b c d e f g h -2

(white to move) 1. Nf3 Nc6 2. d4 e6 3. c4 d6 4. Nc3 Nf6 5. e4 e5 6. Bg5 h6 7. Bxf6 gxf6 8. Nd5 f5 9. Bd3 fxe4 10. Bxe4 f5 11. Nxe5 Nxe5 12. dxe5 fxe4 13. Qh5+ Kd7 14. Qg4+ Kc6 15. Qxe4 dxe5 16. O-O-O Bd6 17. c5 Kxc5 18. Qc2+ Kb5 19. Nc3+ Kc5 20. Rd5+ Kc6 21. Qa4+

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