Possible Clues:

• "But war's ___" (Cowper)
• 'Only --' (NPR show)
• Important barman and Russell admit master between Dublin and Kerry, for example
• "This isn't ___!"
• "It's only ___!" ("Winning isn't everything!")
• Maximum ability, so to speak
• 'I want to play ___' (line from 'Saw')
• With 15-Across, George R.R. Martin novel about rival Powers?
• One's competitive best
• 'Only ___' (NPR program)