On second thought, maybe the scale goes something more like this:
Metroplex is nearly 700 ft and Optimus is around 35 ft. (2 pixels = 1 foot.)
Trypticon's height was based on the fact he's nearly as tall as Metroplex, but slightly hunched over.
Fort Max and Skorponok's size were based on the fact that each of the their heads needs to transform into a normal to large sized robot.
Omega Supreme's size was based on the fact he needs to be roughly head and shoulders taller than Devastator and also the fact that Omega needs to be large enough that other large autobots can easily fit inside when in alt mode.
Devastator's size was based on the assumption that all 6 vehicles that make up the Constructicons are giant mining-type earth moving equipment.
Sky Lynx's size was based on the size of an actual NASA space shuttle
Bruticus, Superion, Defensor and Menasor's sizes were all based upon the sizes of the vehicles they're made up of.
Predaking was a guess. Some comic said 80 ft tall, but that seems a little small if he's meant to take on Sky Lynx. I went with 100 ft because it looks about right. Anyone else have input on this one?
Grimlock is slightly taller than Optimus, so I put him at roughtly 45 ft in height.