I've done a little monitoring myself.. I've never seen a difference.. At cruising speeds my stock intake temps are very close to ambient temps.. With a K&N FIPKII system, the cruising temps are the similar..
At idle on a hot day, the K&N would show higher IAT than the stock intake..
Before you bash me for the K&N, I would only have it installed for days at the track.. I bought it years ago.. Since i've never seen a measureable gain in performance, it stays in the box anymore.. A total waste of almost $400.. It looks cool I guess..
Vehicles with charge-air-coolers will almost NEVER show any IAT cooling with a CAI. The CAC will bring charge temps down regardless of what air filter is being used.
And I suspect that any "performance gains" to be had in vehicles W/O a CAC come from the fact that most aftermarket air filters have a significant increase in intake area, not from any reduction in IAT. (remember that most factory air filters breathe through a relatively small hole, for noise reduction purposes.)