Okay, I haven't heard the R909, but I'll try to answer your Q's.
Since last year I've promised myself that, when I buy a MD recorder, I want to have type-R. It is the best ATRAC I've heard, and if MD can be as good as that I wouldn't want any less
Having said that, the reason I bought the MT770 is that I'm using it primarily for playback. I've still got another recorder for SP, and I want to wait until I'm back in the US this fall, when I can get a cheap deck with type-R. I prefer Sharps for playback.
A while ago, I did an unscientific comparison of the MT770 and the Panasonic MR200 (my usual SP recorder), using Natalie Imbruglia (told ya it's not scientific). The MT770's ATRAC is Sharp's version 6 (the same one from the 877, 831, 821, 722). Sharp goes for a forward delivery; there's more emphasis on the "edges" of the sound, which makes the whole thing sound impressive, but also fatiguing after a while.
The Panasonic's ATRAC is more laid back - just like type-R - as in, they feel smoother around the corners. Both of these attempts to offer an impression of wide soundstage, by placing a bit more emphasis on the lows and the highs. Sharp 6 is actually the most true to ATRAC principles, but compared to these two it can sound "boxed in" and narrow. If you're not listening to modern rock, the other two has a chance of shining through.
So, if the R909's type-R is not substantially worse than the JE440 deck I heard - and it shouldn't be - I definitely recommend it over any Sharp, for recording purposes.
About the motor: The 909's spindle still runs way faster (IIRC, in the 3000rpm ballpark) than any of the Sharps (~1350rpm).