I personally roll with the idea that Fat Boo's power at the peak of his rage just before the split was more or less on Pre-Rosat SSJ Gotenks' level based on Piccolo only stating Boo's body had become better for fighting when he became Evil Boo and was already questioning Gotenks' chances before he came to the Heavenly Temple. Pure Evil Boo would be close to the power of the Fat Boo who fought Goku imo, so CG Galu's getting wrecked in both scenarios.