Jerry  how often do you recommend replacing  orings if everything is set up right?
Would you say the vitron ones will last longer than silicon ones ?

Replace them when they become eroded or flat on two sided.  Some guys replace them every time they remove the head.  Some guys run them for years.  I only replace them when they are damaged. 

I prefer the viton.  Silicone expands when it comes in contact with gasoline, oil, and antifreeze, making it difficult to reuse the o-ring.  When the o-ring expands you usually cannot get them back in the o-ring groove.  Silicone will with stand a little more heat but I think viton is good for about 400 deg. F.  If your head get up to 400 deg. F., you will have to replace a lot of other parts besides o-rings.