IO sets definitely suffer the ED restrictions. If you slot in damage that totals over 100%, you will see significant reductions in effectiveness. The most effective slotting mixes and matches sets, but of course some of the set bonuses require you to go with all one set. You have to balance the normal enhancement benefits against the set bonuses.
I team with the Repeat Offenders.
Slotting a full set of Apocalypse will give you 101.86% Dam enhancement after ED. Note that Set Bonuses do not factor into ED. Also, when you exemplar/malefactor down your Enh % scales down. If you have greater than 100% enh, you suffer less actual drop in performance (you stay near the ED soft-cap for a greater range of levels).
You can see for yourself the prospective effects of ED by using Mids Hero Designer.
ok thanks, I got it now. I need to respec! 
-Listen to my Light!
-MA #1065 "Star Struck"
I need help in understanding something about ED and how this is affected in IO sets. Lets take damage for example in the Apocalypse set. If you put the whole set in the damage % adds up to 145.7%. In reading about ED it says that anything over 100% gives an 85% reduction on multiples of the same type enhancement. Does this mean that sets do not suffer this penalty since each of the enhancements are different? thanks.
-Listen to my Light!
-MA #1065 "Star Struck"