IMO I didn't found any clue that enabling LLC would degrade a CPU. I was playing with Asus Rampage Extreme these 3 months and I always have LLC enabled to prevent significant vdroop.
Yesterday I was accidentally have LLC disabled (E8500 @1.2v, 500x8)
Then when I tried to IBT it the vCore droop from 1.177~1.194 (By MB sensor, never trust CPU-Z) to around 1.134, of course wierd behaviour appeared / unstable / random reboot due to insufficient vCore....