Fastest LCD data throughput 8080 or SPI
The raw speed of the physical interface doesn't really matter all that much, because the effective throughput is going to be limited by the BUSY status controlled by the display anyway. It's probably safe to assume that all of the interface options are capable of keeping the display "busy" most of the time.

The minimum cycle time of the 8080 interface is given on page 61 of the datasheet: 240 ns @ 3.3V. It's the same for the 6800 interface, too.

The 3-/4-wire interface clock period is a minimum of 50 ns (page 65), so in terms of byte transfers, it's going to be roughly 60% as fast as the parallel interface (400 ns per byte).

The IIC interface is limited to a clock frequency of 400 kHz (2.5 &micro;s per bit, 22.5 &micro;s per byte), so this is the slowest option of all.