I own 6xx series B&Ws and can say that the ascends are not as bloated in the mid/low bass area. The 6 series is good speaker, but cant reproduce the same as the 170s
I've never heard them in the same room, but I'd take the $220 bstock 170SE over the older gen 600, and 700 BW series bookshelves.
The only real bookshelves that I've got to listen to in my own home, at least recently, are PSB (various) and MA Bronze. The 170s are better off axis than both IMO. While the PSB is a very good speaker for most people on this budget, I have the same kind of complaint that bandphan does. I think its most prominent compromise is bloated midbass, both in the bookshelves (at least the larger B25s) and towers. However, many larger speakers at this price point seem to have the same fault, to be fair.
The $220 Ascend is a great value right now. My main complaints are the unsexy looks, both being boxy in shape, and the vinyl textured finish from what I remember. Not offensive, but not so sexy either.