In that case, I would say that the wastegate is the only limiting factor to overboosting when you remove the cat. So, if it's adequate, and the spring in it is proper, then it should not be a problem as long as you configure the boost controller correctly.
Aaron Cake recently had a problem with the "Natural boost" setting on his car, where the controller was not engaging because he dialed it in for 13psi, and the natural pressure that the turbo made was around 12.4-12.6psi. Make sure you have this set correctly as well.
PS: how much time and money did you sink in that setup? That's nice!