EL 8 is calculated from the fact that EL 1 is 2 orcs and each doubling of monster numbers is +1 EL, ergo 128 orcs is EL 8.
A 5th level sorceror can decimate a horde of 128 orcs. 4 fireballs (or ice burst for 30' radius) will kill just about every orc. A rapid shot archer will thin out the...