The tubes as described pass cool air down to down draft carbs that are shrouded by the tank , the nature of the design creates a heat trap in there and cool/cold air creates better HP. OK, I am running FCRs with stacks so they are getting a direct benefit but I guess the air inlet on the airbox is right where the cool air is coming in.
Never been out on a crisp night and the bike goes like a whippet ? Another benefit how little it may be is the fuel in the tank is getting some hint of coldness too - just watch any WSBK or MotoGP on a sunny day and you will soon see them covering the tanks, again cold fuel makes better HP - a common belief after filling up a full tank is you think that petrol station has good fuel - its not, its just you have 15litres of cold fuel.
Had your tank resprayed ? make sure you line the bottom again with heat shield otherwise your heating the tank well up !
Must check condition of mine - wondering if this is another hot start cause 
Just my 2p worth
Aside from that, it's not a ZXR unless it has the hoover tubes
Unless you mean you like to see the revs bounce off the limiter for a few seconds 
