No real/one answer. Margin fishing like most techniques will depend on what the fish want on the day. First its location, how deep/close to the bank will the fish feed confidently? What's the margin profile like?
Then you have to get the feeding right - groundbait/micros/4mm/corn and how do they want it - cupped/thrown/lot/little
Then hookbait - corn/maggot/4mm/6mm pellet
Presentation - overdepth (up to 3 ft sometimes)/dead depth
I like to think I am a fairly good exponent of margin fishing but there are days I struggle to find the right combination.
Once fished a lake where the fish were spooked by the line below the float. Every time a fish touched the line the margins would boil and empty. Eventually fished a 6 ft rig in 3ft of water pinning down the last three foot with 3-4 No.6 shot.
Never come across a similar situation since but its always in the back of my mind.
Carp in Gibbos only average about 2-3lb the odd one bigger. I would feed micros and fish whatever gives you most confidence they are not that fussy, feed about a foot away from the bank and fish as tight to the bank as you can, you won't get liners and foul hookers like that 
If you have a match on Gibbos then fish out a bit it will probably be a bit tight for margins save for a few pegs. A short line will work and shallow works as well plenty of silvers in there and carp too. Depending on numbers if you're good at shallow fishing that could be an option.