I emailed Asus support asking what size of SDHC card the 32 Gb Infinity can use and here is their reply:
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Dear Valued Customer,
Thank you for contacting ASUS Customer Service.
My name is Joe and it's my pleasure to help you with your problem.
Sorry,the TF700T only supports the 32gb SDHC SD card now.
I am very thank you for contacting ASUS and providing your feedback. Your information has been documented and forwarded to the appropriate contacts for further review and improvement.
If you continue to experience issues in the future, please do not hesitate
to contact us.
Best Regard
Joe
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Not sure if this statement indicates that a future firmware update might allow larger cards but it seems for now, 32 Gb is the "recommended" size. And "Joe" never did answer my question about which brand of card is better suited to the Infinity.