The Catalyst 9.10 driver pulled a win on both the tested R600/700 graphics cards with the linear gradient blend test through JXRenderMark. The Radeon HD 3850 was approximately 17% faster with the Catalyst driver and the Radeon HD 4650 was 28% faster with the official AMD Linux driver.
The Catalyst 9.10 driver lost with the 12pt Text Grayscale operation with this test profile that heavily stresses the X Render extension in X.Org.
Turning to the GtkPerf test profile to look at the performance of different GTK widgets, the GtkComboBox performance was roughly the same between the two drivers and two graphics cards. Of course, the raw GtkPerf numbers do not necessarily correlate to the real-world performance of Gtk-based applications.