I'm assuming the bindings are Atomic also. So far as I can tell, that's a somewhat unusual model, that's similar to the other Atomic Xentrix (race or otherwise) models, but with a lower DIN range, going from 2.5 to 9.
I think those are intended as bindings for lighter women. They might be intended as kids' bindings ... which makes me wonder whether the skis could be a junior model too. If they're full-on kids' bindings, they might only fit with the kids' boot lugs, though that DIN range is sufficiently high it'd normally be for kids big enough to be using standard-adult-DIN bindings.
That seems like a very unusual ski/binding pairing. You'd think that somebody strong enough to drive a SL11 would need a higher DIN range than 2.5-9. Perhaps somebody swapped it into this Frankenski configuration simply to get rid of stuff they didn't want?
It looks like there have been a few different iterations of the "259" binding in Atomic's line. There's been a Race/Xentric version (which is what' I'm guessing is on these skis), as well as (apparently) a 259 in the Device line.
I agree with DtEW that the paring of a 259 with a race ski (as opposed to a women's ski like the "Balanze" line or whatever, or a race carver, like the SL9) seems a bit odd. As I mentioned, I'd guess that the 259 was used by a kid, like a J4 or a smallish J3. While it wouldn't really make sense to put a J4 on a 155-165 cm "real" (even if not race stock) slalom ski, sometimes parents get length-confused.
Back to the OP's questions:
If you're going to set them at 7, they should work just fine. That setting seems at least to be a reasonable one for you for recreational skiing. If you want to race on them, you're might find yourself hitting the top of the DIN range. I don't know if that's a disaster, but if these were primarily a race ski, I'd probably try to snag some replacesment 412s.
I don't know, but I'd be surprised if they won't adjust to a 310mm sole length. Assuming they're the Race/Xentrix, the heel and toe piece connect to one another with a metal band that has a series of holes for different sole lengths. It's possible that, in making the 259, they made the metal bands short on the assumption the users would be smaller. If you unscrew the screw in the center, under the foot, that holds the whole thing together, and look under the plastic cover, you should be able to read the marks and see if there's a problem pretty quickly. You also might need to remount to the ski, but if it's an ordinary SL11, there shouldn't be any issue with having the appropriate holes for your sole-length pre-drilled into the plate.
As far as the "quality" of the binding, I'd suspect it's no different from other similar bindings, other than the lighter spring. It might not have as many fore-aft positions that you can slide the binding into (I know the 412 has one less than the 614).
Note that, as with other Atomic bindings, there is the "recall issue" (and also the "heel problem," which may be the same thing). There are posts on these.
Yeah, I though this was a unusual combination myself, hence this posting. The seller isn't being very responsive and detailed in his replies, so I'm a bit hesitant. However, since he is only asking 150, I'm pretty interested, but a little worried about the set up. (As a side note, from the pictures I'm going to guess that these bindings are the Race 2.59). As well, is anyone able to comment on SL11s? I want to use them as an all mountain, calmer ski, basically something that I'd use for skiing with younger cousins or just taking it easy. Should I possibly consider SL9s instead?
The issue brought up about the DIN at 7 and recreational skiers raises another question I had. Though I am a recreational skier and don't race, I do ski hard and rather fast, should I consider increasing my DIN?
SL11s: not what I would ordinarily consider either "all mountain" or "calmer," though I suppose that depends how you want to use them. They've got a lot of sidecut, and if you lay them over in any sort of a attempt to carve a turn, you will typically wind up doing a lot of quick, short turns. You can lazily sideslip them down the hill, but I guess there are better skis for that. For one thing - and here I may be being a bit idiosyncratic - I prefer a longer ski for general use, and would use something as short as 165 (which I think is as long as the SL11 goes) only in an effort simultaneously to acquire the quick turniness of a slalom ski, which (again) is anything but "taking it easy." The only countervailing thing to note is that, as compared to other race skis, these are bit damp, so at least they're less inclined actively to fling you toward the next turn.
The SL9 is also a quick, super-sidecut ski. It's softer, a bit more foregiving, and you can find it slightly longer (170). In the longer length, it also runs wider at the tip, which I suppose makes it a little more versatile if you want to run it through crud, though there are certainly skis more intended for that use.
On the binding setting: if you're skiing at 7 and not getting premature releases, don't fool with it.