Agree with pretty much everything you wrote, except for speed. The HD650 is ever so slightly lacking in speed, this is noticeable in very complex music. 

Agree about the Sennheiser myths. Most of the criticism of these headphones comes from people who listen to headphones with lots of attack and sometimes harsh bright treble. So they are criticising the balance and accuracy of the headphone. Because these headphones give a smooth and accurate sound they are labelled as boring, the sort of headphones that put you to sleep. The speed of these headphones is a little slow compared to other types and the soundstage is relatively intimate. They can be driven without an amplifier but you may require high volumes if the signal levels are low. To get the best from these headphones you need amplification. They do offer slightly enhanced bass and rolled off treble which makes people describe them as dark, so there are more neutral headphones than these. To get more bass extension and sub-bass usually involves big expenditure, you could try Beyerdynamic's DT990 which has more bass/treble extension.