Yip, all you get is an extra custom slot (but not after every prestige, you only get an extra slot every 2nd or 3rd prestige after the first one). No different perks/weapons etc. What you have unlocked now is all you get, all that happens is you loose everything and unlock it again. I have done restige 4 times now. A buddy of mine has done it 14 times... doubt I will prestige again.