A few thoughts:
- DIN is a standard. It isn't supposed to be vary from one binding model to another, and certainly not from one ski model to another. It may vary from individual binding to binding, a little (one hopes), but unless you actually have somebody test the binding, you wouldn't know that. The setting could also be inaccurate if the binding is misadjusted (e.g. if the forward pressure is insufficient, the binding may release more easily than indicated by the DIN setting), or if your boot is damaged or really old (e.g. if the lugs of your boot are misshapen due to wear, it could make the binding release either more easily or less easily than indicated by the DIN setting).
- As noted, the piece of data you're missing to use a standard chart is boot-sole length. On the DIN chart I'm looking at, you could get 5-3/4 as the recommended Type I setting if you've got a really long boot sole.
- If 5 worked for you with one set of bindings, it should work on another (unless the old bindings or new bindings were out of spec, which -- again -- you can't tell without having a ski shop test them). If they're not prematurely releasing, there's no reason to set them higher.
- If you want to explore the issue fully, you might take both your old and your new skis in and have a shop test both of them. Whether this is worth the effort and cost, I don't know.
- I can twist out of bindings set at 9 standing still (this is higher than I usually set them).
- Since the bindings you have don't go below 6, you have two choices: (i) set them at 6, which (as compared to your existing skis) should reduce the likelihood of premature release and increase the likelihood of injury (assuming both are in spec and properly adjusted) or (ii) get new bindings. If you get new ones, it's preferable to get something where you're fairly close to the middle of its DIN range. I'm not sure, but I'd guess the Neox 310 would fit the same holes, so you wouldn't have to re-drill the ski.