Ive owned all three.
All ZMFs are above your budget,but are the best of the bunch. Ive owned the Auteur,Atticus and both of the Verite,open and closed. The Auteur is the most neutral of the bunch,and would be the closest to your HD800s,but IMHO the Auteur slays it. Much more body,texture and musicality than the Senns.
The Atticus is the most opposite of your 800s. Thick & warm, w/ slamming midbass. Its a superstar if you like hard hitting headphones with a healthy lingering decay.
Verites are a step up. The Verite closed is the best headphone Ive ever heard,bar none. It does nothing wrong,and is a genre master. Every single type of music Ive thrown at it,the VC just delivers in a wonderful manner. It has the widest sound stage of any closed back Ive ever heard,and its 3D imaging is breathtaking. Great mids,fantastic midbass,even better sub bass. It is similar to the HD800 that it lets you hear every single detail,and if an album is poorly mastered,you will know it.
The VO has a more wide open,airier sound vs. the VC. Identical tonality as the VC. It sounds more laid back and chill,whereas the VC is very dynamic and powerful.
EDIT: I should add that all ZMF love tube amps. The VC is the best of the bunch with solid state,accentuating its speed and clean sound. Other than the VC,all other ZMF headphones really need a tube amp before you get the full effect.
The LCD-2 has great sub-bass,but the mids sound boxy to me and the treble is really missing. The fazor version was created to help the treble,but in the process you lost some of the bass. If you opt for the LCD-2 try to find a pre-fazor version.
The HD650 is like a poor mans Atticus. Midbass hump,a bit veiled sounding. Good for blues and rock. Too slow for faster stuff. The sub bass rolls off too early for my tastes. Very narrow staging and can be quite uncomfortable due to a strong clamp.