I found this in the 950 manual:
You can use the following memory cards with the Reader:
Memory Stick DuoTM media
Memory Stick DuoTM
Memory Stick PRO DuoTM
Memory Stick PRO-HG DuoTM
Memory Stick MicroTM
SD Card SDHC Card
Sony’s Memory Stick DuoTM media of up to 32 GB has been tested to work with the Reader. But the proper operation on all types of the Memory Stick DuoTM media is not guaranteed.
SD card of up to 32 GB has been tested to work with the Reader; however, not all SD cards are guaranteed to work.
The M2TM Duo-size adapter must be attached to use Memory Stick MicroTM media in a slot for Memory Stick DuoTM media.
The file system incorporated in the Memory StickTM limits the capacity of a file to be transferred to less than 4GB.
Data over 123MB cannot be recorded in a single session.
Standard-size Memory StickTM media cannot be used on this product
The maximum number of songs that can be recorded in the Memory Stick PROTM media is 65535.
So it doesn't seem like sony is suggesting any specific SD cards. And it doesn't say anything about speed differences. On a side note; whats the difference between Memory Stick duo (only created by Sony) and SD cards?