From my experiences with conventional flat tappets, you will see cam/lifter wear at ~370lbs/in 'open' spring pressure. Again this is with conventional flat tappets and cams. Now with shubecks, I wouldn't run anything less than 400lbs/in 'open' spring pressure. I rarely worry about valve spring pressure 'on seat' or 'closed'. I choose my springs according to open pressure and let the closed pressure fall were it does. Again, this goes for flat tappets only.