Dennis @ PerfectForms
A form connection is very fast and from a database perspective no different than a get field from other instance. They both pull data from the database. In this case the database is all the same, it is the PerfectForms database.
I don’t understand your process fully, but if you want to use a Get Field from Other Instance object, you will still probably need a form connection to get the instance ID of the other instance. That is unless the global variable is the same for every user. If it is the same for every user you can create a global variable form with one instance and reference that instance ID in the Get Field from Other Instance behavior object in your form.