Hi Guys, Ive just gotten around to ordering the 4k upgrade for my 2 X70's and now I'm £740 lighter (I wish we had the rebate)

I need to order some 128gb cards as my 64's wont quite be enough, but do I need U3 SD cards or will I be OK with good quality U1's??

Not sure if the 4K recording on the X70 is 60Mbps or 100Mbps. If it's only 60Mbps you can use U1 cards. If it's 100Mbps you need U3 cards. Price difference is another matter to consider. If it's significant or you or your clients can't really see the difference between the 60 and 100Mbps files then U1 cards should be enough.

I have the AX100 and since the free firmware upgrade almost a year ago I've been shooting only with U1 cards at the lower 60Mbps as I think the IQ difference between the two bit rates is too small to be bothered with.

There is no 100mbps option in the X70's 4K mode... yet.

Get U3s regardless and avoid Sandisk Ultra and get Sandisk Extreme Pro cards,

Please consider that the X70 only records a maximum of 600 clips on a card. If your clips are not extremely long, a 128 gb card is a waste of money.

If you are trying using the higher bitrates (100Mbps) the camera can record, it will recognize whether you're using a U3 card (or not) and not allow the camera to record - at least that's how the AX100 and RX10M2 operate. I suspect Sony put lockouts in the firmware so that there's no risk of "user malfunction" due to inadvertent use of "low spec" cards - preventing recording fails and customer support "issues".

I've found Lexar (Micron, so should be good memory) SDXC cards to be fairly reasonable in price, especially for the 95Mbps/"633x" cards, and sometimes the "1000x"/50Mbps ones.

I'd never worried that much about card specs, but once I started using higher speed cards, the performance difference for stills and file transfers was pretty noticeable, thought I'm not convinced that lower rated cards "can't" record the larger files produced by higher bitrate modes successfully...

Bottom line is if you need to buy new memory cards, probably better to spend a little more to get higher spec cards.

Thanks guys for your answers - I think I'll get the U3 versions they're basically £50 as opposed to £30 & if the X70 ever get 100mbps I'll be set.