I have both so I'll try to help out as best I can. Keep in mind that these are relative comparisons to each other. Since I've only listened to so much, it's hard to make sweeping comparisons across the board.
I'm pretty convinced that the k601 earpads lend to both greater bass impact and reduced soundstage. By reduced soundstage I am referring to an awkward layering of frequency bands, not quite muddiness but definitely not clarity.
Given that, the k701 extends lower (but not with more power), and there is more of an accent on the treble that pushes that frequency region toward your ears. I suppose this is the sparkle that people refer to, but I'm not too up on the terms. For comparison, k601 treble is seated behind the mids in terms of spatial representation.
The 701 feels like it is powered properly out of my gcha at all levels, with my k601 I feel like I have to listen louder than normal to get the correct "feeling" out of my music.
I used to use the k601 religiously, but since the cable went out on me, I came across a friend's 701 and I haven't switched it out much lately. I'm writing this as I switch back and forth during songs. I suppose if you wanted the short story, 601 vs 701 is trading between the intimacy and clarity of sound.
I've had many hours on the 601s, but I haven't found much of a sonic change, except maybe a SLIGHT smoother transition between bass and mid. To answer your question, yess bass impact is better, but it's AKG bass.
Hopefully I was of some help