If you had the CB client Cryptic said you can patch it up to the retail version, I'm not going to bother reloading the game from steam once i pay for the pre order. The only reason im going steam or Digital is to get the keys / activation. I did the same with the last two beta's I was in.. =)
You can purchase from steam, get the key and then just use the CB patched client to OB without using steam. Just use your login info and bobs ur uncle. No need to go thru steam just because you bought from there.
1st off anyone who knows a bit about steam fileing system is that they dont put stuff in the normal way we are use to. so there for it will NOT update old files and it will a completly new install of the game in a different file and there for take up another base of 8GB til you update once your updated it will move up to almost 12GBs of extra wasted space. I know this for a fact 1 I have and use steam for some games and 2 I have looked to see where steam places there stuff.