SP 120A can support modified motor as low as 3.5T with turbo (However, with such low turn, turbo is meaningless as you cannot boost it too much). You will need
1. Make sure your ESC is prostock or GT2.0
2. download the newest firmware and load the proper firmware into the ESC. It should be 100528mod or 100528stock. Of course you need 100528 for 7.5T.
3. Do not use any advanced timing in your motor's endbell
4. Beware of overheat when setting the turbo (supercharge). 7.5T is not that low in term of modified.
5. Beware of gear ratio. Overgear will burn!
6. Finally, you still need to bear the risk. Suggest you send mail to SP for suggestion. If I were you I will set it from the lowest and monitor the temp and speed one by one.
Ps. I am using the same ESC but not dare to do so. I am using 4.5T. I am looking for cheap 6.5T. Hope that you could share your result afterward.