I was implementation about this scenario :
AP ( WDS ) --- AP ( WDS ) = Option 1
AP ( WDS ) --- Wds Slave = Option 2
This option have different function, I think speed is the some.
AP (WDS) Option 1 allow client to connect to both AP, both AP must be at some channel.
Wds slave allow to connect to AP like client but with full layer 2 transparent bridge using wds but other can connect to the device in wds slave mode, also scan for signal based on scan list not need to be on some channel on establish connection. If you have Mikrotik device try also station bridge that allow transparent layer 2 bridge without creating additional wds interface.
More information http://wiki.mikrotik.com/wiki/Manual:Wi ... tion_Modes