A review comparing EFR and GT ballbearing surfaced up the internet sometime ago showing the picture below claiming the EFR to have a bigger ballbearing cage. The truth is both the GT and the EFR has bigger cages but they start at a diffrent turbocharger frame. The border catridge is actually a GTX3582 which oftenly is compared to a EFR8374 and also the GTX3076 with the EFR7670.
The GT/GTX series is divided to 3 frames while the EFR series is divided to only 2 frames.
GT25/28 Frame1, GT30/35 Frame2 , GT37,40,42 Frame3.
While in the EFR series , all EFR up to EFR6758 shares one frame while anything above it shares a bigger catridge. In comparison the EFR7670 sits in a bigger frame while GTX3076 sits in its seconds frame thus EFR having a bigger cage but also a beefier shaft which also means heavier. No doubt the GT series are proven till at high boost capabilities till today despite it counterparts differences. GT30/35 based turbos are one of the most used turbocharger in the Motorsport industry where some with billet wheels surpass the 800hp range.
EFR big cage vs GT small cage
GT small cage vs GT big cage