You don't get max gain on a CAI or smoother flowing exhaust by themselves, you need both. Picture the engine as a large air pump. The easier the gasses can enter and exit, the better. If one side is restricted, you won't get max flow through the other....
IIRC, a CAI or exhaust system is supposed to add around 8-10 HP, but even though the two work best combined, the combined total HP is probably closer to around 16 HP or so. Based on early posts about both, mods like these just don't seem to be linearly additive.