As is often the case the many of the features that improve a new release are back-ported to the previous release. With careful tuning the performance of 11.7 can be very similar to that of OpenEdge 12.
BUT - this process eventually stops and we are pretty much there now. I would not expect any new features that appear in OpenEdge 12 to find their way back to 11.7. That ship has sailed.
And there are features in OpenEdge 12 that are already not present in 11.7 For example: multi-threaded servers, server side joins, and online table reorg.
The conversion from classic app server to PASOE is a bump in the road but everyone that I know who has done it is happy with it and all the reports that I hear say that it was pretty easy to accomplish.
Sticking with 11.7 for another 10 years is not a good alternative.