[10HORT]

I've had one on mine since it was purchased in 2016 and even during WOT, I have yet to experience any problems. I have seen some Hemi engines torn down in my local FCA dealership's shop and the first two cylinders in the block (including pistons and correlated head ports) showed a darker residue than in the remaining cylinders and head ports. Although I have not seen one torn down that had run a catch can, my thought is that even at 40% as mentioned (40% is better than 0%), a catch can would reduce the amount of blow by coming into the intake manifold. Just to review the basics, I read these articles and afterwards, I still believe that a catch can is beneficial.
Positive crankcase ventilation (streetrod101.com)
How an Oil Catch Can Works, And Why You Might Want One (roadandtrack.com)

I have seen engines torn down with almost equal miles on them (50K and 47K) with and without a catch can. The one with the can was a lot cleaner than the one without. The intake on the canless one was loaded with oil, compared to the pretty clean one with one. The front two cylinders on the canless one were pretty nasty looking and were probably causing the Knock Retard that engine was having just before the timing chain broke. The one with the can had pretty clean cylinders, not Chevy LS1 clean, but for a G3 Hemi, pretty good. The one with the can was a stick car and had the heads removed to replace a weeping head gasket on the passenger side.

My '08 Charger R/T had a can, my '10 Challenger R/T had one, and my present car does too. I ordered the can for my present car before I even bought it.

 

[10HORT]

I don't see any possible negatives to a catch can, unless you forget to empty it