@MatthewInwards
One thing to keep in mind - delegation and record limits are two completely different things, but are related.
Record limits determine the maximum number of records that can be "fetched" at one time. If you have a list with 20 records in it, and a record limit of 50, then you will always get all records. If you have a limit set to 10, then you will only get 10. The lower your limit is, the more performance you will see, but, obviously, with impacts.
If you have a limit of 10 (let's pretend that is the maximum you can have) and need all 20, then you will have to devise a method to make multiple "fetches" to the data source and store them locally.
Delegation is like asking someone for something. If someone has a collection of coins organized by coin type (nickles, dimes, etc.) and you ask for all the dimes, they will hand you a box of dimes. If you can only carry 10 dimes (remember our pretend scenario above), then they will only give you 10 - you'll have to come back for more. If you decide you want to have all the 2017 dimes, then if the coin collector will "support" that request, then they will give you back all the 2017 dimes. If there are only 5, then you are in luck because you can carry them. If they DON'T "support" giving you coins by year, then they will say "sorry, can't do that for you, but I can give you the whole box and you can find them yourself." Okay, not a problem...but, we can only carry 10.
So, delegation - if we say, give me the 2017 dimes, they say can't do but here you go with all of them, and you can only take 10, then you will be looking (Filter) only through the 10 dimes...if you find one, that's great, but there might be more in the box that you didn't get because you didn't go back and get all the dimes.
So, in the PowerApps world - if we raise our maximum number to the max of 5000 we're now carrying back more data for any function that has to be done by us. But, the pure fact that we have to do this Filter (or other non-delegable function) on our own means that the performance will suffer.
Remember, it would have been much easier and faster if the coin collector could have just given us the 2017 dimes...very fast. If we now have to make several trips to carry the dimes back and then have to sort through them ourselves, it is going to take some time.
I hope this is a clear analogy and is helpful for you.
