farming elite at lvl100 on hardcore

short:

I am on my way to the hardcore archivements. But lost already 2 chars in ultimate.

Now i start farming with my new level 100 in elite. What are the
disadvantages to do this? Sure most of the mobs are 20level below me but what does that mean to dropchances and loottables?

That means:

Less legendaries. Lower level of items.

Level of loot will be level of MOBs +/-10.

So if MOBs are on 79 level - that will drop loot between 69 and 89 level.