How much of a difference is there between the two a ( Mod/Fast tip and Extra Heavy Power) over a standard fast action tip with (Extra Heavy power.) as I. Needed for only flipping and forging but no punching in the 5 pound weeds.

An EH / MF rod is going to bend deeper into the blank before it shuts off than the EH / F.    How much is going to depend on the rod in question, some MF rods lean towards the moderate side more and other lean towards the fast.

It depends on the makers definition of XH & ModF. Both are subjective. The fact you state explicitly no punching leads me to lean toward sticking with a fast action. I go mod f in a punching xxh

I'm going to agree with DVT, go with a fast action rod if you're flipping and froging.  Punching I would say Mod/Fast or Mod only to help keep the fish pinned in the weeds and help absorb some of the short line fight.  Froging you want to move those fish quickly and a rod that shuts down a bit quicker such as a fast action will work best.  Some even like extra fast, but I personally prefer fast action for what you're looking to do.