I wouldn't go above 2 and leave preview on zero or maybe change it when you want to check out the smoothness, the preview subd'd makes the programme slow down and I don't think above 2 is needed for rendering, it usually warns you above 2 anyway.
edit to add- odd thing happened when i posted this, i got a red lined box come up saying it needs moderator approval?
edit to add- odd thing happened when i posted this, i got a red lined box come up saying it needs moderator approval?