I didn't say anything about mirror mode not being able to skip the initial detection phase.
Was just pointing out that you can use the official client on mirror mode. Since you said:
what file extension should i save the configuration as? when I load a saved configuration it just logs out. When I save a config it saves as "all files". no file extension is set.
I suggest testing it out yourself. There are lots of factors when talking about banrates.
While you're at it, go read some guides that are posted in these forums. Trust me when I say they really help alot.