[Scott Fraser]

now please correct me if i am wrong, but:
although option 1 gives me flexibility in terms of mic placement, it does
not seem too convenient because i need two microphone stands and it will
most probably be a great pain to drag this all along.

Yup, it's a big array & hugely inconvenient in field use. You want
portability.

option 2 gives me more flexibility, because i can mount mkh-30 and mkh-40
piggyback on top of one another and it results in that i only need a single
boom, which is much easier to carry along and operate with. i also get M/S
output which is automatically decoded into conventional stereo by my lunatec
v3 preamp. i also get better focus and isolation to the sounds directly in
front of me. in addition, i can possibly get additional jobs with field
recording for film, since this setup seems more directional.

All this is correct. For field use you really want convenience, &
having both mics in the same zeppelin is the way to get convenience.
Another possible approach, not available with any Sennheiser mics, is
to mount two Schoeps CMC, Neumann KM100, or AKG 451/460 bodies
parallel to each other in the Rycote & use the available swivel joints
to aim cardioid capsules off in an XY configuration. Or use active
cables to remote the capsules in a Schoeps or Rycote ball gag. Of
course the more accessories you add, the more expensive the whole rig
becomes.

option 3 seems to give me a lot of flexibility (variable polar pattern on
mkh-800) and a better quality/dynamic range (mkh-800 - opinions?)

My opinion is the MKH800 is a great mic at a price nobody can
realistically afford.

at a seriously higher price. anyone has ever tried mkh 800?

Yes, it's wonderful. I would never consider purchasing one.

is it possible to record sounds above 20,000 hz with mkh-800 + v3 setup? will mkh-800 pair be significantly better than mkh-800 + mkh-40?

I think, given your desire to use this equipment for field recording,
that any improvement in quality deriving from using an MKH800 will be
entirely academic. Outdoors is amazingly noisy. I've had many, many
field recordings in wilderness areas compromised by distant aircraft,
vehicular & nautical engine noise. I wouldn't sweat the minute quality
bump possible by going from an MKH40 to an MKH800.

Scott Fraser