I have been told that when float fishing, I should use hi tech / pre stretched mono as a hooklength as it has a lower ø and the stretch comes from the mainline when playing fish.
I have also been told to use braid as a mainline when feeder / tip fishing as It gives better bite indication with little stretch.
Does this mean with the stretch taken out of the mainline when tip fishing with braid I should use normal mono to give some play/ stretch back to the setup? Or just keep using 'hi tech' pre stretched hooklength material with little stretch in the setup?
What to use as mainline and hooklength will depend very much on where you are fishing and what your target species are. The following are my own thoughts, others may disagree.
To me braid is for silvers (non-carp) fishing where bites can be delicate. The stretch free braid will transfer any movement at the hook end to the tip. Mono can dampen the tip's reaction because of its stretch. This effect will be increased as casting distance increases. The need for the main line to stretch is reduced when catching silvers because they are, mainly, not that large and the rod will deal with lunges. I would expect a softer action rod to be used for silvers and so the lack of stretch using braid mainline will be replaced by the action of the rod.
In addition a "high tech" hooklength can be used for the same reason as the fish being caught will almost certainly not be able to apply sufficient force to break the line. Being thinner you can get away with a higher breaking strain.
Carp however rarely leave the angler in doubt as to whether they have taken the bait or not. The stretch in mono therefore is not an important consideration when detecting bites. But the power, and size, of carp mean that the stretch in the line aids the cushioning of lunges in association with the rod's action.
As a consequence a high tech hooklength is cushioned by both line and rod. Again, a high tech line of high BS will be used, often greater than the BS of the mainline. What the high tech line lacks in material "toughness" is made up by its overall strength.
To sum up. I would use braid mainline for smaller silvers who's bites can be delicate, mono for carp and larger silvers like big tench and a high tech hooklength for both.