Hi Hockey9. I have exactly same problem. My new(second hand) X5 runs very slowly with an sd card fitted, if the card is writable. It speeds up if SD card is removed or switched to read only. Cannot see the SD card using either X% file manager r laptop via sync, unless SD card is switched to read only. It occurs on a 256m Puremedia card and a Memorex 1Gb card. Both ok in my camera. Ir an SD card is fitted switched to read-write, and the X5 turned off, you canot start it up again except with a soft or hard reset.
I know you had this problem. Did you ever find a solution? There don't seem to be any answers on the web or this forum.