I made Sudden Strike not negated by non-total concealment to give it at least some edge. I think in retrospect that's not nearly enough; being in the condition to Sudden Strike should probably let you just plain ignore non-total concealment.
Then again...I kinda hate how easily concealment screws rogues and also thought of letting them SA in it. But then I'd have to buff Sudden Strike again to make up for
that.
Making it identical to SA is definitely simpler, I did like the idea of keeping it separate and with its own benefits, though, based solely on being stealthy instead of also flanking. It's much easier to get flanking than flat-footed / lost Dex to AC, of course...