The SMT TCU looks at several values, in order to downshift correctly:  Target RPM, current RPM, RPM cut.  From what I've found out in testing, you can rev them out as high as you want without much of an issue.  However, coming back down, the system may refuse to shift, as the 'target RPM' may be over 7200rpm (where the stock motor limits) and that will cause problems.
 
Having said that, if you're losing boost as low as 5k rpm, there is little point in winding the motor out much past around 6k anyway - all you are doing up there is generating excessive heat and general wear.

Not if - When :P
 
Feel free to PM me and we'll discuss the car's requirements and go from there :)