I have owned the HD600 and currently own the the 1440 and have auditioned the 650 several times. So will take a shot at this.
The HD650 is a warm to dark sounding headphone that can have a bit of veil in the midrange if not properly amped. The bass is deep but not particularly punchy. The treble is nice but I find it doesn't produce cymbals as accurately as I like, I find it to be a bit pingy.
SRH-1440 is warm to bright sounding headphone. It doesn't need an amp but will benefit from one. The mids are very clear and present and forward. The bass is not deep but is punchy and present. The treble is well extended and clear and does cymbals very well in my opinion.
The sound stage is similar on both.
The 1440 is slightly more comfortable in my opinion but both are comfortable. The HD650 is lighter.
The 1440 is more versatile due to it's lower reliance on a quality amp and is good for most music genres but is very detailed and can be aggressive for some people.
The HD650 will need a good amp to sound it's best but has a dark luxurious sound, some would find it's signature to laid back.
For me the 1440 is as close to perfect I have found.[/QUOTE
I just purchased the Shure 1440 and compared them with the HD650 and agree that the seinheiser is warmer but close in sound to the Shure. It feels like I can hear every detail in the Shure and if the source recording is bright to begin with, then the overall music can be extremely bright. Just purchased the shures for $269 new at alto music and for the money can give the $1k focal elear a run for its money