A Chinese blogger published the first Nikon MC-CF660G CFexpress Type B memory card benchmark on Weibo (the new card is currently in stock at Adorama, Amazon, and B&H). Here are the benchmark results:
The highest read is 1700 + MB/s
The highest write is nearly 1500 MB/s
The card can write 300GB continuously without a drop in speed.
“The measured maximum read is 1700+MB/s, the maximum write is close to 1500MB/s, and the continuous 300GB random write has no speed drop. 8K60p N-RAW on the Z 9 can record to full card (about 15 minutes).” (source: Weibo)
“The MC-CF660G is a CFexpress (Type B)5 memory card with a large capacity of 660 GB. It realizes a maximum read speed of approximately 1700 MB/s and maximum write speed of approximately 1500 MB/s. It is particularly suited for video/still shooting with the Nikon Z 9 full-frame/FX-format mirrorless camera.”