Possible Clues:

• What the letter O is?
• End of a close race ... and what the last part of the answers to starred clues can literally be
• Very close race, and what 17-, 26- and 41-Across have in common
• Racetrack nail-biter
• Racetrack drama
• When two fairly matched cameramen raced, it came down to a ..
• Race decided by a camera, or what the start of 17-, 26- or 42-Across literally is
• Glossy or matte
• Close end of contest that's decided by final shot
• Snap decision at end of race?