I think that's one of those deals that you don't do til right before the #6 pick on Draft Day. If Suggs is there, you pick him.
If Newman, Robertson or maybe even Leftwich is there, you think about it.
If none of them are there, you leap on that trade like a blue bunny.
The key to doing that deal (if Suggs isn't there) probably becomes a function of how the Cards rate other players who might be available at #17 and #18 (I'm thinking McDougle, Woolfolk, Henderson).
If the Cards feel the dropoff between those guys and what's available at #6 isn't all that much, maybe they make that deal. (The sticky wicket, however, is that there doesn't seem to be a consistent concensus as to where these next-echelon players will be drafted - the danger being that the Cards would trade down only to find that the guys they want are already gone).