For me, my old eyes, and my P226 40 cal, the standard factory stock 6 front, 8 rear, makes me shoot about 2-3 inches too low using a "Center Hold" sight picture.
I'm calling SIG today to order an 8 front, hoping that 8 and 8 will work better for me and the "Center Hold" sight picture that I prefer.
I'm sure it is an individual preference thing ... what works for me may not be best for you.
Ken
Ordered the TFO Front Sight in Size 8