A few months ago someone asked about routing a 3/8" deep 1/4" slot. A
number of replies were that it was too deep and risked breaking the bit.

I said I had done it plenty of times and never broken anything.
Well, today I broke a brand new Freud doing a 7/16" slot. Got about 8"
across some luan and the darn thing twisted off.

So, I was wrong. (well, still never broke it on 3/8") Fortunately I just
bought a dozen of them at an auction for $4 each.