That much boost the gate is fine.
Now if you were trying to run 4-6 psi you might need s larger gate. Gate is just a bypass vent. The higher the boost the less you want to bypass. At 20 you are coming to the end of that turbo.
Have you tried higher?

The standard Borg t4 83 would give good flow and less back psi.
It's a large housing and large ar potential.
Requires a larger down pipe config.

 

Go ahead and put the big turbo on, you will sooner or later eventually :p

 

Rick I've had it as high as 22psi but IAT's were almost 160. ECM was pulling 3* of timing for KR and 3* of timing for IAT. So she was a bit out of her element.

 

Yea time for a bigger turbo.

 

Is the 83mm Borg exhaust housing a 4" outlet?

 

Bigger turbo will need bigger down pipe.
3.5" is What we normally send with t4 borgs.

 

I have a 4" downpipe for the s480 with the 96mm exhaust wheel, just curious if the outlet flange is the same for the 83mm exhaust wheel.

 

Yes as long as it's a t4 Borg.