E-5 is very little life in it because of attitude control system failures that require greater use of propellant to keep the satellite stabilized so I don't think it is going anywhere except to a higher grave orbit. The E-8 satellite is available after E-11 is launched so it could be moved to any of a number of other slots including 119, 129, 138 or 148. After E-11, the next satellite is E-14 a spotbeam that I believe was scheduled to be launched in 2009 to the 119 W slot. This information was reported in a Dish financial report a few quarters back so things maybe changed.
I don't think it normally takes that much fuel/propellant to move a satellte from one slot to another so an estimate of the loss of two years of life on E-1 and E-2 is very conservative.