I2C is a low speed bus designed for transferring small amounts of data. Usually used by sensors and devices which don't produce/need much data. I2C was designed to function bidirectionally over 2 wires and talk to many devices on the same bus (each has a unique 7-bit address). SPI is a higher speed interface which requires more wires and supports higher speed devices. Neither one is suitable for HD LCDs due to the amount of data required to drive them.
I2C - default speed 100Khz, 'high' speed 400Khz, newer devices support 1Mhz and 3.4Mhz
SPI - no default speed, typical devices support at least 4Mhz and up to 100Mhz. Inexpensive LCD displays can usually handle 20-40Mhz.
A 240x320 LCD with an SPI interface usually maxes out at about 30FPS update rate (~32Mhz SPI). A higher resolution LCD will obviously have more pixels and full frame updates will take longer.