You really havent added to my first question, have you had any luck with a 64gb card?
Well at least I wont be out $50+ if I bought the sandisk and it didnt work. You are covered by the eBay Money Back Guarantee - if you received an item that is not as described in the listing.
Actually, I had purchase this card for my phone, not my X930BT. So, I can't tell if it would have worked or not.
As for the "Money back guarantee", yeah, I got caught in that trap too. The card was $17 (it wasn't listed $50+) and PayPal said "Well, the seller can't be reached. You're entitled for a full refund! Just return the item to the seller's address and provide us with the tracking number to prove you sent it". Cost to send the fake card with a tracking number: $17!
I ended up buying a Class 10 32gb Kingston micro SDHC for $27 and it rocks.