If people follow the most efficient way to finish E7, you should be able to knock it down with more than 5 mins remaining. It only takes a few hours to level an S rank from beginning till end of custom.
If getting skills already seems hard, I can tell you guys now that trying anything above OC5->OCEX will take 10 times more time (depending on your luck that could even be an understatement). I have already failed getting from OC6 to OCEX on my V2 Buster 3 times, that is 25000*3=75000exp wasted.
As for items like 100% OC (Which only works for OC1-5), and is not available in shop. These are usually given in the normal events that Kr holds (eg, collecting sticker events, pvp events, etc).
Last edited by RacerX; 11-29-2009 at 01:45 AM.