I really need to be able to justify any amount of overlap if I move to the SE.
There is overlap, but SE has a much more complete instrumentation at a fair price and contains the excellent new Vienna Instrument, which is the way forward for VSL - I imagine all their products from now on will run on that engine.
If sample overlap is a sticking point I suggest you wade through the respective articulation lists available here (maybe print them out for ease of comparison) to see exactly how much is duplicated. I doubt another user would have time to do that for you!
One thing worth bearing in mind - if you buy the SE extended version you will have a complete orchestra (with several alternate solo instruments, wind and brass ensembles and three different string section sizes), saxophones, keyboards and two guitars. No important instruments are missing and some rare ones are included, so you will be able to tackle a full orchestral score. The same can't be said for the Opus bundle.[/quote]