Our apologies for the delay in response.
Regarding your questions:
1. You can still export your MIB to the 6.60 version since we're "backward compatible" in that regard. Basically, what this means is that as long as your MIB is created at a lower version than your app, there shouldn't be any problems when it renders. However, it's when you upload a MIB version newer than the app version where you can possibly run into problems (i.e. features not working, etc). Always remember the app version ultimately rules in this regard.
2. If you want to create specific 7.10 MIBs, then yes, your apps will need to be updated within the marketplaces to that version as well so everything is on the same version number and there are no discrepancies. Please note we always recommend keeping your app as up-to-date as possible. The best rule of thumb to follow is to try to match your MIB version with your app version or at the very least, make sure you MIB version doesn't exceed your app version. Once again, app version is more important than MIB version but ideally, they should match for best performance overall.
3. As mentioned above, we do not recommend uploading newer MIB versions to older app versions as the discrepancy can cause problems (i.e. features not working, performance issues, etc).
Hope this helps.