Optimize item detection and passthrough

I will have an object, which will need to detect GameObjects will particular class and return them for processing. This is a demo script that I've crafted:

Code (CSharp):

1. public class PerformanceTest : MonoBehaviour
2. {
3.  
4.    class Player { }
5.  
6.  
7.     void Start()
8.     {
9.        // Say, there's 10000 objects
10.       var playersFound = CheckIfPlayerNearby(Vector3.zero, 500.0f);
11.  
12.       // foreach() {} and conitnued processing
13.     }
14.  
15.  
16.     List<Player> CheckIfPlayerNearby(Vector3 center, float radius)
17.     {
18.        Collider[] hitColliders = Physics.OverlapSphere(center, radius);
19.        List<Player> output = new List<Player>();
20.    
21.        foreach (var hitCollider in hitColliders)
22.        {
23.           Player pc = hitCollider.GetComponent<Player>();
24.           if (pc != null) output.Add(pc);
25.        }
26.  
27.        return output;
28.     }
29.  
30. }
31.  

Here are my questions:
1. Is there a way to optimize script above? I couldn't forgive myself unnecessary 10 frames or 50ms CPU lost due to lack of optimization on this one. Especially when this will become a highly reused code. I know I could decrease the radius of detection but the point is optimization of script, not game hedging.
2. How do I use

OverlapSphereNonAlloc

. My IDE screams that I should use it instead, I tried for a second, and I adjusted the parameters but I somehow can't get it done.

Edit: I've just found out that I can use layerMask to specify the layer. Do I specify the layers that I want it to check, or do I specify the layers I want it to ignore? If I want to use multiple layers, do I simply use

|

?
Edit 2: I don't quite care about precision, for all I care the actual shape of said sphere could be icosahedron.

 

It will be much simpler and more performant to just use a Sphere Collider set as a trigger collider with the appropriate layer collisions set up in physics settings and just use OnTriggerEnter and OnTriggerExit to detect the player entering or leaving.

 

I got that, but I can't see a way to tell OnTriggerEnter to focus on a single layer. I don't want to mix up Physics settings either because this won't be the only physics operation executed in the game, other physics interactions must remained untouched. Or do I have to do a tag comparison manually?

 

They should really add an example to the docs. Here's an explanation.