This is what I do. For example if I'm in 6th and gradually slowing with traffic to about 40mph I'll still be in 6th at 1500rpm, but as soon as I'm at 40mph or 1500 whichever comes first I downshift. Same with the other gears. Lately I've had a bad habit of running 3rd lower than 1500rpm and having to quickly downshift in the middle of a turn or something because I grabbed the wrong gear. If you are just barely on the throttle and aren't going above like -4 or -3 psi of boost it won't hurt anything going that close to 1500...but like said above if you have to speed up, downshift enough that your rpms get to 3k or so. That way your engine takes the blunt of the acceleration before your turbo has to kick in. And if you need to really take off just downshift to whatever gear puts you at 4+ and release some rubber into the wildNo tune here...I try not to let the RPM's fall below 1500 whatever the speed limit is.