Don't confuse boost threshold with lag.. If your boost threshold is 2600 and above, then thats where you need to keep the revs above if you want power.. 'Lag' is the time it takes it to produces full boost from the time you open the throttle fully, when you're ABOVE the boost threshold..

If you want to lower the boost threshold without changing the turbocharger, the easiest way is probably to add a bit of nitrous to it. 25 shot or so.