Minor - P4 Per http://docs.mongodb.org/manual/reference/configuration-options the default value for journalCommitInterval is 100 or 30. Starting mongod from 2.6 RC0 using the MacOS binary (or something I build myself) I get 0 when it is not set in the config file.
> db.adminCommand({getParameter:1, journalCommitInterval:1})
{ "journalCommitInterval" : 0, "ok" : 1 }
When I explicitly set journalCommitInterval to 200 in the config file I get 200
> db.adminCommand({getParameter:1, journalCommitInterval:1})
{ "journalCommitInterval" : 200, "ok" : 1 }
This is confusing because a non-zero value really is being used given this code in dur.cpp
unsigned ms = storageGlobalParams.journalCommitInterval;
if( ms == 0 ) {
// use default
ms = samePartition ? 100 : 30;
}