Nice photo's Chip. According to Roland Vink's Nikon- encyclopedia ( http://www.photosynthesis.co.nz/nikon/specs.html#50-xx ) focus-throw is only 150 compared to the 190 of the E 75-150. Perhaps the close-focus of 1,30m is a factor?
Yes, when comparing the focus throw you also need to consider the close focus limit: the 75-150 has focus throw of 190° to 1m, the 50-135 has 150° focus throw to 1.3m (190° with macro mode at 50mm setting). It turns out the focusing "speed' is pretty similar between the two lenses - just look at the focus scale starting from infinity and you will see the the distance scales are spread out a similar amount.
I have both lenses but used the 75-150 more often: it has slightly more reach, it's smaller and lighter, takes the same 52mm filters as my other AI primes, and it focuses to 1m through the entire zoom range - no special macro mode - and being able to focus to 1m at 150mm is more useful than 1.3m at 135mm or 0.6m at 50mm.
The 50-135 on the other hand is built to higher standards, has a greater zoom ratio (quite useful on DX) and the filter does not rotate when focusing which is handy when using a polarizer.