I'd like to add this from the thread I linked:
Lets see if this works...this picture gives a good idea of the size of the new lakes.
The picture is not entirely accurate in respects to Sahara, which looks forested. We'd get mostly savannah with some areas of vast rain-forest.
However, observe that the two mega-lakes together are bigger than the western Mediterranean.
Because its so hostile, its easy to forget how huge the Sahara is.