None of them stand a chance. Palhares has decent take downs, but let's not over exaggerate them. His take downs are not remotely good enough to take GSP down.
GSP has proved time and time again that he has the best MMA wrestling in the game. Palhares wouldn't be able to take him down and would get picked apart on the feet.
See thing about under estimating Palhares is that he is one Crazy fcuker who would be willing to keep move forward and risk taking a hard shot and possibility getting KTFO to at least try for the TD.
See what I thought Shields needed to do in his pathetic attempt, at least come the championship rounds when it was obvious that for as long as it was standing he was just going to get outpointed all night long, was take bigger risks, hence move in and take him down whatever the cost, hence running straight threw that jap and big overhead right and just hoping it misses or does at least not connect right and if it does land hope that your chin can take it and you are still conscious.
That would be my strategy for guys like Palhares/Shields anyway once all else was failing fcuk it, don't back off risk having to take his best shot and just don't stop going forward for the TD till ether you have his legs to work the TD or you are out cold.