i dont use regex and thereforei dont know it sorry
all i can help with is that which i know .. if someone else comes that knows it great .. but untill then all i can do is offer the best advice i can come up with.
that jacked up server might only send 6 nicks per line but mirc can read alot more than that, i sugest u maintain a hash table with the list of nicks in it, parse each one (with the loop)
after parseing the 3rd one, send all the nicks u have to mirc in 1 socket, then restart the list, and after 3 again send, and repeat untill the end raw is sent then just send whatever u heave left over
that will speed it up some ? .. not as much as u might like but its beter than nothing.
sorry i cant be more help, but i'd be suprized if regex was all that much faster.. it wont take mirc all to long to parse 6 nics out of a string .. and u will have to call the identifer the same number of times even if u used $regex .. although $regex may be faster than the loop .. i doubt that the difference will be that noticable personaly but its hard to say