Rob Galbraith, who has been testing and comparing memory card performance for ages, recently published an article with read and write speed comparisons of XQD and Compact Flash on the Nikon D4.
He reports that write speeds of up to 92 Mb/s with XQD allow for uninterrupted bursts of 160+ full resolution JPG fine @ 10 fps, while the fastest CF card, the 1000x Lexar Pro 32Gb is no laggard either: 62 Mb/s. The latter would be good for bursts of up to 140 JPG fine.
In other words: the D4, combined with fast cards allows for between 14 and 16 seconds of continuous shooting at its maximum frame rate!
This makes the D4 + XQD about 3 times and the D4 + 1000x Lexar CF twice as fast as the D3X in combination with its top-performer, the Sandisk Extreme Ducati 4Gb, a CF card which he reports to max out at 30 Mb/s with JPG and about 32 Mb/s with RAW (NEF). Being the D4 the first camera on the planet with a built-in standard Ethernet RJ-45 100Base-T connection, he also tested the D4's WiFi (with the WT-4) and “cabled” performance, which he reports to be “a little” disappointing at between 4.8 and 5.6 Mb/s.
For more information, click here.
See also: Dpreview - Nikon D4, first impressions.