Image replies limits are apparently fixed.

4chan_x.user.js

@@ -4370,11 +4370,11 @@
           case 'v':
           case 'co':
           case 'mlp':
-            return 251;
+            return 250;
           case 'vg':
-            return 376;
+            return 370;
           default:
-            return 151;
+            return 150;
         }
       })();
       return Main.callbacks.push(this.node);

script.coffee

@@ -3467,11 +3467,11 @@ ThreadStats =
     @imgLimit =
       switch g.BOARD
         when 'a', 'b', 'v', 'co', 'mlp'
-          251
+          250
         when 'vg'
-          376
+          370
         else
-          151
+          150
     Main.callbacks.push @node
   node: (post) ->
     return if post.isInlined