For me enabling Textured XRendering made almost nothing
gtkperf witout TexturedXRendering:


GtkEntry - time: 0,09
GtkComboBox - time: 2,82
GtkComboBoxEntry - time: 2,22
GtkSpinButton - time: 0,32
GtkProgressBar - time: 0,21
GtkToggleButton - time: 0,86
GtkCheckButton - time: 0,77
GtkRadioButton - time: 0,96
GtkTextView - Add text - time: 1,47
GtkTextView - Scroll - time: 0,48
GtkDrawingArea - Lines - time: 2,64
GtkDrawingArea - Circles - time: 0,49
GtkDrawingArea - Text - time: 3,37
GtkDrawingArea - Pixbufs - time: 0,50
---
Total time: 17,21


And with:

GtkEntry - time: 0,10
GtkComboBox - time: 2,79
GtkComboBoxEntry - time: 2,22
GtkSpinButton - time: 0,31
GtkProgressBar - time: 0,20
GtkToggleButton - time: 0,80
GtkCheckButton - time: 0,73
GtkRadioButton - time: 0,92
GtkTextView - Add text - time: 1,47
GtkTextView - Scroll - time: 0,48
GtkDrawingArea - Lines - time: 2,59
GtkDrawingArea - Circles - time: 0,45
GtkDrawingArea - Text - time: 3,24
GtkDrawingArea - Pixbufs - time: 0,50
---
Total time: 16,79


I think I will keep it enabled, maybe it spears me few ms