Amatsubu, I'm in the same position as you and asked the same question more or less, a few weeks ago. here's a few observations I've made over the past couple of years:
there are, IMHO, no decent stereo mics on the market for anything under about £800. Yes there are some mics about and I'm sure a few people could name some on here, but all of them have in my opinion, some really annoying quirqks. When I say stereo mics, I mean handheld. Added to that, you then need a sepperate device for recording. Again, a lot of these have quirks.
Binaural recording is great, but only really if you listen back through headphones. I have a set of binaurals, the bmc3s and honestly whilst the head image is lovely, it never ever translates as well to speakers. Additionally, it's very hard to protect against wind noise, cable movement and russling. The last 2 can be done but it's a bit of a gamble. Example, I wear a croakie to affix the binaurals to my glasses. No one else has issue with this that I've heard of, but for me, my hair crackles against it every time I turn my head. Binaural is good, I'd just advise considering something else as well if you want to play back on speakres and get the same effect.
For my money right now, portable recorder with internal mics, I'd go for the zoom h6 because: It has a reasonably low noise flaw on the internals. Certainly you're unlikely to notice it in most situations unless the area around you is almost totally silent. The noise it does exhibit is, oddly enough, like a very low wind through trees, which might work well in your case. Please don't misunderstand me, I'm not saying you can hear it all the time in fact the majority of the time I have to look for it on my recordings and never come across it. I hate repeate hate noise flaw with a passion so I'd not use it if it were there. It has 2 types of mics that come with it, an ms wwhich is... interesting, and xy which are nice. It also has different modules including a shotgun you can plug on to it which might be exactly what you need. It also has some surprisingly really good preamps, 4 of them in fact, which you could use for plugging in additional mics later. My point here is that you'll have a lot of options to play with and can find what works best for you. You will likely need a rycote and suspension to get the most out of this for £100, but it's not entirely necessary, I just recommend it.
Finally, it has a line input, which you could use for plugging in binaural microphones. The batteries on internals are truly insane. I've been recording with it everywhere since the end of November and only changed the 4 AAs once. I like that it has 4 AAs as well, wop them out and then stick some new ones in in under 30 seconds if you're good, and you can always get AAs wherever you are. The bootup time is amazing, it's all up and running in about 4 seconds for me and that is absolutely crucial when you're recording.
The whole thing comes in a little case which for you might be really handy.
I'm not sure I agree re the sony d-100. The internals are... ok, but for the price, I'm really not sure. Also, and I realise some people may really disagree with this one, I've never had anything from sony, bar a playstation which actually lasted and it makes me very nervous about buyhing anything. You have their own brand batteries which are going to be hard to come by unless you have spares as well. The whole thing just makes me nervous. Maybe I need to play with one when it comes out and have my mind changed.
The one thing I'll say about all of this gear, is that vyou've not really considered wind protection. None of these recorders work very well with that. The ls-100 is just utterly pointless in this regard, don't even consider it if you're going anywhere windy. I've tried all sorts of things and the wind gets in there. You can even blow into the hold switch on the side and the wind comes in. Just no. If you're going to be recording somewhere very very windy like the sea, a rycote blimp is what you'll probably need and unfortunately that will set you back quite a bit, not to mention you'll need an external mic for the job.
So, some random thoughts for you there, hope it helped, drop me a line with any questions, I'll let you know if I ever find something I like without quirks