No Offense taken. Proper testing is ALWAYS appreciated. That is just what Ive seen in my many games as Sivir.
Good to know about DI (not that its easy to SS or anything) and I havnt been in a game with karthus since the new graphic (been smurfing teaching my new friends, side note: OMG its rediculous what you can do at that level and get away with it. Nice change to the tryhard games I have to play on my main). But Im nearly CERTAIN that was one of the spells I counted as "free mana" along with the other "easy" spells to shield (Dark Matter and Even Horizon being the top 2, nothing better then laning against veigar in mid).
Just figured Id give you a heads up, and some of that, I know 100%, but it will be better for readers if you test it as well (as there will be no doubt at that point).