Well I don't know where the stats are, but I've read an article or two noting Rose::DB is quite a bit faster than DBIx::Class with about the same learning curve from what I can remember. Perhaps I can dig up some more information and share it.

I haven't done anything with Rose-DB yet, so I can't comment on the learning curve. From discussions in #dbix-class and on the DBIx::Class mailing list I remember that RDB's speed advantage comes from less methods who contain much more logic. While this brings a speed gain (less method calls) it sacrifices easy extensibility, which is one of DBIx::Class' big advantages.

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Ordinary morality is for ordinary people. -- Aleister Crowley

Well, it depends on what you're extending. For example, RDBO has a very flexible framework for defining new column types, encapsulating inflate/deflate, custom DBI bind_param()s, type-specific attributes, and custom SQL for select, query, and insert into a single logical unit. DBIx::Class is still working on some of these features, and the lack of a standardized way to add support for new column types has led to less support for "rich" column type handling.

As in any large collection of code, there are really only a few performance-critical parts of RDBO that are aggressively optimized. The vast majority of the code is quite modular.

That summary is a bit out of date. Both RDBO and DBIC have improved a lot since then.

After considering DBIx::Class, Rose::DB was recommended to me. One thing I can't figure out is why there is the requirement that tables have a primary key. I'm working with a legacy DB in which many tables do not have a primary key. Is Rose::DB simply unusable? Or is there a workaround I haven't found yet?