Correction:
Fluid intelligence is just the ability to think and reason abstractly. The higher your fluid intelligence, in theory, the faster and more efficient you become at thinking abstractly.

One study shows that people with very high fluid intelligence have closer connections between neurons which allows them to reach conclusions faster. Another shows that the brain organizes itself in a more efficient manner allowing them to use less brain power to reach the same conclusions someone of lower intelligence would take longer to come to.