It is really a trial and arrore method especially when you are not using a nute where others have already been successful, but I know that one goal when growing is to make it as simple as possible with out losing out on productivity. If you know your plants you may experiement for a couple res changes and just listen to your plants IMO.
Adieu
PS, also the larger the res like in your case, the more room you have to make mistakes, but I know that mistakes are the last thing someone wants to make in their grow.