Amusingly enough, Pathfinder PLA doesn't seem to be able to turn you into a Sarrukh at all as Sarrukh is a Monstrous Humanoid and the whole Polymorph-line conveniently lacks a spell that gives you Monstrous Humanoid shape. Alternatively, you could say you turn into it and gain nothing. Pathfinder Polymorphing in general only grants the benefits offered by the appropriate Polymorph-spell; Alter Self is the closest to Monstrous Humanoid-forms, which would gain you...+2 Str and the look of a Sarrukh. Yes, that's it. So of your list:
"SLAs, stats, natural armor, movement, darkvision, casting"
You'd gain Darkvision. Yeah, Pathfinder Polymorphing is pretty weak...then again, given it's quite broken in 3.5, that's kinda understandable.