diff --git a/README.md b/README.md
index f2f2dd6..fe404f0 100644
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+++ b/README.md
@@ -68,7 +68,9 @@ Rotate the map manually with the rotation control, or lock it to your player cam
 
 ### Icon Controls
 
-When zoomed out past a configurable threshold (default 40%), car icons are hidden and only locomotive icons remain. Locomotives scale up automatically so they stay easy to spot. A separate option hides MU trailing units, keeping just the lead locomotive per consist. A blinking red EOTD dot marks the rear of each consist, giving you a quick sense of train length without cluttering the map with car icons.
+Each car icon on the map is a live Canvas element. On a large session with many cars visible, the rendering cost adds up - testing showed a **3-12 FPS improvement** when zoomed out over a busy portion of the map with culling enabled.
+
+When zoomed out past a configurable threshold (default 40%), car icons fade out and only locomotive icons remain. Locomotives scale up automatically so they stay easy to spot. A separate option hides MU trailing units, keeping just the lead locomotive per consist. A blinking red EOTD dot marks the rear of each consist so you can still gauge train length at a glance.
 
 All of these options are available from the gear menu Icons submenu on the map toolbar, or from the S³ UMM settings page.