There is nothing in the engine itself that uses more memory or CPU depending on the layout size, so it's true that the layout size itself has no effect on performance. However if you fill a larger layout with objects, it's more likely to have a lot of objects, and having lots of objects can reduce performance. But in that case it's the object count reducing performance, not the layout size.
yes, I made a test with 20'000 x 20'000 and is working perfectly
another, I'm making game with 8000x 2000, with the same range for 3 tilemap, and 8 layer with 3 background.... and the fps are 61 in iphone5s
I suggest to try and look in debug... make a different way is the best method to see which way is better