3.2 LCD runs really slow on 8 bits, so most of 3.2 LCD don't use 8 bits.
What is the basis for this statement?
The size of the screen has nothing to do with the speed. The resolution of the screen has an impact. Since most 3.2" and 2.4" displays use 320x240 pixels they will be exactly the same speed provided they use the same bus width.
The difference between 8bit and 16bit communication is also minimal as the 8bit only require a few clock cycles extra per write.
Get a 2.4'' LCD with 8 bits, so you have enough pins for other functions like SD card and touch panel. and only use a 3.2 LCD with arduino MEGA.
This statment is mostly true, but it looks more like electrodragon are trying to push their own merchandise than trying to be helpful.
It is best to use 8bit modules on Arduino 2009/Uno, and move up to a Mega of you need a 16bit module. This is only needed because of the number of available IO pins, and NOT because of the speed.
PS! The above statement is not fully accurate, as the speed also depends on the LCD panel refresh rate, controller speed, etc., but it is accurate enough for this context.