Regardless of whether you run manifold vacuum or ported, vacuum goes away with your foot in the throttle. So "firewalled" the vacuum drops off under power and you are left with whatever initial + mechanical you put in it AKA somwhere around 35, and that is what you want
On problem that can occur with ported is when you (and us) start to swap around carbs, etc you can run into a situation where the carb produces too much vacuum at part throttle, and you can get into ping. I used to have this problem running either GM QJ or Holley spreadbore on my TQ manifold on the old 340, and later, on a 360 with a TQ manifold. These were both mild engines with either stock or stock 340 cam
