TDB and SDB concurrency questions

I've been reading through the Jena concurrency HOWTO ( http://jena.apache.org/documentation/notes/concurrency-howto.html ) and wanted to know a bit about how it applies to TDB and SDB.

Let's say I have two Models, MyJenaModel1 and MyJenaModel2. My understanding is that if these are memory models (collected together in a dataset, say), I need to ensure multiple reader or single writer access, or I'll run into issues. Presumably if I want to do a SPARQL query that could get data from either of the models, I also need to read lock them both.

My questions are about how this applies to TDB and SDB. In TDB, each thread creates its own dataset as below:

Dataset dataset = TDBFactory.createDataset(location) ;

If Thread1 and Thread2 each access MyJenaModel1 through their datasets, are the model objects I get back the same? I.E. do I need to ensure MRSW on the model, or is that unnecessary? My assumption is that I don't, given the content of the TDB transactions page, but I wanted to be sure.

The same question goes for SDB - if I use connectNamedModel to MyJenaModel1 in different threads, am I getting back different model objects, and thus free from having to enforce MRSW?

Finally, a slightly different question. If I have a set of operations that I want to perform inside one transaction that involves creating/deleting a bunch of different named graphs, what's the best way to do that in a running SDB system without doing separate writes for each named graph (and thus presumably having a lot of round trips to the DB)? Can I do this using SPARQL Update, or is it achievable using the bulk loader?

Thanks a lot for your time!