I would recommend the T50 over T40 for the ever so slightly extra detail.

First, I like both T40 and T50, I will keep them and I am waiting for the T20 to arrive

To me, the T50 is like a mixture of the X2 and AD900x

T50 is leaner, clear, flatter and has a little wider airier sound stage with a softer but a little extended bass

Also If you are into headphones mods, flatter T50 might be more flexible because the vent is not sealed like T40

I would say T50 is closer to neutral character most audiophile prefer

n’t feel uncomfortable about the stock ear pads