Possibly more info than you want to know, but as potential benefit to others...
For drum hardware, Yamaha changes a model "number" to identify notable (design) changes, and appends a letter A, B, etc. to denote a change in manufacturing factory (that occasionally have also included some minor changes).
Typically, the first digit(s) identifies the series, the next digit(s) identifies the version within that series, and (if needed) the final digit(s) identifies a sub-model. Here:
-- CS-7xx denotes a 700 series Cymbal Stand,
-- the -x4x and -x5x denotes difference design versions within that series, and
-- the -xx5 denotes a boom model (whereas -xx0 denotes a straight stand).
The primary differences between the CS-745 and CS-755 cymbal stands are:
Production: 2001 - 2008
Boom Tilter: Top-Bolt
Cymbal Tilter: Offset (was straight in the previous CS-73x model)
The differences in each of these tilter designs can be seen in the attached photos and the reasons for the changes were:
1. Side-Clamp boom tilter: for greater clamping pressure on (smooth) boom arm w/o marring it
2. Straight cymbal tilter: for greater strength (re-implemented from previous models)
The Offset cymbal tilter was initially implemented to allow for more compact collapsing as the center rod can be pivoted parallel to the arm rather than at 45(ish) degrees. However, it proved to be a little too weak for some so Yamaha re-implemented the Straight style on the -x5x versions of the 700 & 800 series, and only kept the Offset on the lighter weight 600 series. They also subsequently implemented the Offset on the ultra-lightweight 3 series (aka Crosstown series).
Nonetheless, the CS-745 are still solid cymbal stands and are often mixed with the CS-755 in people's hardware configurations if there are any concerns.