What I have is 1 smart object which exists of several smart layers: Adobe Camera Raw layer & 6 several Nik google filters (color efex, sharpening pro, define, viveza, analog pro, silver efex pro). When I want to open the smart layer it loads very slow and it photoshop freezes quite often. I have the newest Mac book pro with 500GB SSD, 16GB internal memory, i7 processor with the newest OSX Maverick. Evertime it freezes I have to shutdown Photoshop and restart it again. It works after retrying but it happens quite often during a day. What I also do is copy the smartobject to a new document of a new photo. Then I drag the smart object with all existing smart layers to the new photo (which is a smart object) and photoshop also freezes when rendering the smartlayers.