How could I streamline this script to find Finder items faster?
I tested your code on my OSX 10.9.5 and saw no issue. It took 2 seconds (delay included).
So, for me, the code is correct.

What is your version of OSX ? (Maybe a bug ...)

You probably already know that but to investigate more on the part that slow the script down, you can use the following 2 statements :

-- Put this before the code you want to test :
set t to (time of (current date)) --Start timing operations

... your slow code here ...

-- Put this at the end of the code you want to test
set total to (time of (current date)) - t --End timing


Sorry, I can't help more.