In my opinion, Harrisons always over rate their carp rods.
Go for at least 1/2lb heavier in the desired TC.
On the seperate issue of PVA bags at 80 yards, then this is a long way to chuck a loaded bag.
I'd say that bag or method feeders at this distance would require rods of between 3 and 3 1/4 lb TC, unless you're owed some favours from your respective deity.
On the other point of whether 2 1/2 TC rods are suitable for large carp, then this is very difficult to answer as it depends on the waters you fish, not the size of the fish in there.
I've landed upper thirties off the top on 1 3/4 lb rods and 8lb hooklengths in clear water, but on another lake I fish where the carp only just make 20lb, then I would not go in with less than 2 3/4lb rods and 15lb line because of the weed, zebra and pea mussels and snag bushes.