There is a huge 6-part thread on the DR-70D (beginning
HERE). Not having the time or inclination to go through it all right now, my recollection is that the preamps between the DR-70 and DR-60 were found to be fairly close to each other in terms of quality and noise; if someone has more concrete references, I'm happy to be corrected. I also feel that either one would be a step up, slight or otherwise, from the Sony M10 in terms of the preamps. Good reference page here from Avisoft, no listings for DR-70 and DR-60 but I think the rumor was that they are just as good as the DR-680 preamps. >
http://www.avisoft.com/recordertests.htmI'm really not a fan of Tascam as a whole but I bought a DR-60D(mkI) on a lark when I found a deal too good to pass up. I don't do the type of low-noise effect and foley work that you do, SDAdam, but I've been pretty happy and pleasantly surprised with the DR-60.
A caveat that you should be aware of with the DR-70 is that it can be very finicky when it comes to SD cards; Tascam maintains a list of supported cards and contends that the recorder will only work well with the ones on it. There are many pages in the aforementioned threads dealing with this aspect of the deck. While some users find that they get exemplary results with the DR-70, there are others who are at wit's end with its idiosyncrasies.
Finally, comparing the Sound Devices products with anything else mentioned in this thread is an apples to oranges scenario. SD gear is built like a tank for professional applications (with a price tag to match) while the other brands and products discussed here are pro-sumer at best; not that they're bad, just in a different league. FWIW, for what you would pay for a brand new MP-1, you could probably find a used MP-2 or MixPre on eBay, here in the Yard Sale, or elsewhere.
Good luck and keep us posted on what route you go.