Two categories of intelligence
I propose dividing intelligence into two categories: "sufficient" intelligence, and "extra" intelligence. Sufficient intelligence would be intelligence that you need to solve a problem correctly, so long as it can be solved by applying normal reasoning. Extra intelligence would be "flashy" stuff--speed of thought, special talents like music or athletics.
Sufficient intelligence would be measured in terms of defects--how far short of perfect do you fall. Extra intelligence would be measured however it is reasonable to measure it--speed would be measured with a speed measurement. Someone with perfect sufficient intelligence would perform every mental task flawlessly, though he might take a long time and he might not be very insightful. There's no such thing as "perfect" extra intelligence, but someone with high extra intelligence might do things quickly or with insight. There can be many kinds of extra intelligence.
It's like the idea of a universal computer. A universal computer must be capable of performing all logic functions flawlessly, and it must have an unlimited memory to store results in. This is sufficient intelligence: the ability to grasp concepts, the ability to remember concepts, the ability to work with concepts correctly. Extra intelligence is: do you have an MMX instruction set? What's your clock speed?