On the contrast thing , for me it's more enjoyable switching beetween HD650 and DT880 . It's what i am doing now , my HD600 is at friend's home for some months for longue terme evaluation and peraphs ending to sell it to him .
If i had to keep only one headphone it would be the HD600 , T1 is for me not worth it in comparison to DT880 unless i had some extra cash . Furthemore i prefered the HD600 in many ways to T1
(naturalness , tonal balance , timbre accuracy etc)
So i can understand why wahsmoh found HD600 and DT880 somewhat similars . Also depending on the system used , they can be more similar/different sounding , on my O² the difference what no enough to keep both , but it is with HD650 as said before) .