I can't find any listing for the MKH18s anywhere, including the Senn website - are you sure that's the number?
The Schoeps 641 is outstanding for interiors and with good wind protection many exteriors as well. You might want to consider partnering it in your kits with the Schoeps CMIT for those times when you need a shotgun outdoors.
If you want to go with a 4xx shotgun from Sennheiser, go with the MKH-416, the mono equivalent to the 418-S. Dialog should be mono. The CMC6/MK41 combo is in most peoples' minds the cream of the crop for interiors.
I like the option of M/S work with the 418 but curious what would be a good companion to the CMC6/MK41 combo for exteriors? I dont like mixing brands, so I'm mainly referring to which capsule I guess. Also, do you prefer MK41 or the "V" for typical dialog?
Well, many many mixers have no problem using a 416 on exteriors and a 641 on interiors. If you really get heartburn from mixing brands, then spend the extra $800 or so and get the Schoeps shotgun for exteriors. Feedback on it is that it is good, but not $800 better than an MKH60/416 or the CSe3. Honestly, get over the concerns about mixing brands. It really isn't an issue as long as you are talking quality mics (i.e. never mix the ME66 with anything.)
The `418s has a good pedigree for the mid capsule (can't go wrong with a `416), but the back-electret side capsule really brings the whole thing down. In other words, its a great mic when summed to mono, but as a stereo mic it leaves much to be desired around the sides. Then again, the figure-8 complement to the MKH30 (an excellent figure-8 compliment to the `416) costs a bit more than a new `416.
When you take into account that the `418-s will only opperate if both capsules are receiving phantom power, it starts looking less attractive as a boom mic. Furthermore, you can forget about internally cabling your boom since the Schoeps uses a 3-pin XLR while the `418-s needs a 5-pin cable.
It has also been my experience that M-S stereo production sound is not at all worth the trouble. Most picture editors don't know what to do with it, and most re-recording mixers will drop the S channel in favour of a nice precise mono dialogue track.
My guess, in regards to the 60,416,cs1,and cs3 is that no group of mixers could agree on a clear winner. I prefer my 416 over my friends 60, and I've used a cs1, which I also liked the sound of, but all of them did a fantastic job. So it comes down to personal taste most of the time. Unless of course there are concerns about RF or humidity, but that is beyond the scope of my use experience.
as a rough breakdown, the strengths and weaknesses of those mics:
416 - bullet proof mic. great quality. off axis is quite coloured as with almost all shotguns, which means cueing is very important. this is kinda the benchmark that most sound people will compare other shotguns to.
mkh60 - designed as the successor to the 416. and although in higher levels of production, it HAS largely replaced the 416 on shoots that arent in extreme conditions, lower levels of production still see more 416s because they cost less but do a comparable job. features a low cut on the mic. in my opinion, better than the 416 - but it DOES cost a fair chunk of change.
cs1 - very short shotgun, designed primarily as a high quality on camera mic, but seeing lots of action on docu shoots as it does a good job of interior AND exterior due to its size and sound. has a very attractive price compared to the other mics here.
cs-3e - the cs1's big brother. lowest off axis colouration of these mics listed, and one of the only shotguns to be directional over the entire frequency response (most shotguns near omni in the low frequencies). this has earned it a rep as having the directionality of mics much longer than it (a la mkh70 and mkh816), however its "sweet spot" is in actual fact quite a bit bigger than the 416/60 making it a fair deal more forgiving in the hands of an inexperienced boom op.
feel free to add to/correct anything i've said guys...