FT800 SPI interface sets MOSI at falling SCK edge. It will be regularly sampled at rising SCK edge. (Standard SPI mode 0 or 3), If the SPI bus involves longer round trip delay, sampling can be delayed to next falling edge, as supported by most SPI host interfaces.
You can check which method involves a larger sampling window margin. FT800 datasheet specifies minimal data hold time of 0 ns. If host samples MOSI data exactly at falling SCK edge, you have zero margin. Depending on the internal host timing, it could happen that MOSI is even sampled slightly after SCK edge, resulting in negative margin (data corruption) in this case. Thus you better use standard mode for slow and medium fast SPI interfaces.