In performance terms, what will be faster, use a BIT(1) NULL (null = unknown, 0 = male, 1 = female) or ENUM('unknown', 'male', 'female') NOT NULL DEFAULT 'unknown' in MySQL MyISAM?

Or this is considered micro-optimization?

[EDIT]

I think I'm going to use ENUM('male', 'female') DEFAULT NULL

Originally asked by: Wiliam on Stack Overflow