well I'm only a lvl 10 thief but I plan to sub RDM because RDM have mainly enfeeblement spells, which at least I think should help a thief.
Pros: Elvaan Thiefs can do MASSIVE backstab damage etc...
Cons:Elvaan Thiefs are really the worst at sneaking etc...
You can think of elvaan thiefs more of the assassin type than the stealing type.