I recently bought a used Nikon SB26 in very good condition . I decided to test out the "SU4" mode on my SB800 compared to the built in flash trigger on the SB26 .
With the SB800 it uses the sensor on the side , next to the battery compartment , to act as a trigger when another flash is fired while the SB26 has a separate flash trigger 'eye'
I set them up facing away from each other and made sure they couldn't trigger each other .
I had another SB800 on my D50 and it was set to 1/128th power in manual mode so I had the weakest possible flash output .
I tried one reasonably close [ about 8-10 metres ] .
They were both set at 1/16th power .
With the lens fixed at 50mm I moved back and they both triggered ok at this distance .
I moved back a bit more until only the SB800 triggered .
Then I moved forward to where they would both trigger ....
At this stage the sun popped out from behind a cloud and only the SB26 triggered - I hadn't changed my distance .
Since I was using the D50 which has the advantage of an electronic sensor/shutter and can synch flash at any speed using 'realsynch' flash I did some extreme shutter speed tests . I mounted the old SB24 and set it at its minimum power of 1/16th and tried at faster shutter speeds .
From what I've seen so far neither system is superior in all ways . The SB26 seemed to handle sunlight better than the SB800 but the SB800 triggered at a greater distance in the shade .