I have the Lawrence of Arabia and Das Boot Superbits.
LOA has a new transfer and has a lot more detail. Das Boot is the same transfer but looks much better. Reason being that the old release was two DVDs and both were single layer. The new one is also two DVDs, but it is duel-layer.
Some Superbits, like Leon, are actually worse than their non-SB counterparts.
I've also heard that The Fifth Element SB is one of the greatest looking titles on DVD, right behind Criterion's The Rock, which IMO has never been surpassed yet.