Turbo has nothing to do with RPM, it's based on exhaust gas volume.
Turbo has alot to do with RPM. BUT, it depends on the turbo of choice. But, the larger turbos don't get up into their efficency range until the higher rpm range for example: full boost at 3500 rpm until 6500. Then the boost will begin to fall off. Again, this is all dependent on turbo selection.
