
The VE, in order to maintain a max RPM limit, starts cutting the fuel off after so many RPM's before flat lining at the springs tension.
The thing to worry about when selecting the turbo is what RPM's you will be pushing most. If all you do is tow and occasionally play, the smaller turbine will help. If you race constantly, get the bigger one. At higher RPMs, the smaller one will "choke" and get hot.