Also the 90 looses zero space to a overflow, it is drilled similar to a glass holes.
I hate to say this also I agree with John if you have the footprint for a 4' x 2' tank that I would go straight to the 120 I have a 90 right now and I will tell you that 18 inches deep is not deep enough. If I had to choose between the standard 90 and the cube I will take the cube, but there is also one other thing that has to be thought about if you are going to put T fives with your led you will only be able to use 24 inch bulbs which unless I'm mistakin are only 18 W they'll never be enough light to get to the bottom of the tank.
Do yourself a favor and go straight to the 120
The standard AGA protrudes about 4.5" or so. But they can be ordered with corner overflows. The Marine land and Deep blue tanks are standard with corner overflows. Or you could drill the AGA and install a glass holes kit or some other type of overflow