MyMoneyObjectContainer served as double cache presumably for DB storage. For XML storage I see it as redundant, because it has its own cache and after latest changes in KMM it's also redundant for DB storage.
Methods in MyMoneyObjectContainer returned its values as dereferenced pointers thus making it difficult to use compiler optimizations.
Committing transactions to MyMoneyObjectContainer consisted of clearing and refilling whole cache, which isn't very efficient.
Despite observed inefficiencies and removal of MyMoneyObjectContainer, I had not experienced any speed up.