diff --git a/bench/churn-sweep.csv b/bench/churn-sweep.csv
new file mode 100644
index 0000000..2d57e9f
--- /dev/null
+++ b/bench/churn-sweep.csv
@@ -0,0 +1,22 @@
+structure,size,latency_ns_avg,latency_ns_med
+MapArray,100,0.03,0.03
+Dictionary,100,0.00,0.00
+Map,100,0.00,0.00
+MapArray,250,0.05,0.05
+Dictionary,250,0.00,0.00
+Map,250,0.00,0.00
+MapArray,500,0.09,0.09
+Dictionary,500,0.00,0.00
+Map,500,0.00,0.00
+MapArray,999,0.16,0.16
+Dictionary,999,0.01,0.00
+Map,999,0.00,0.00
+MapArray,2500,0.42,0.42
+Dictionary,2500,0.01,0.01
+Map,2500,0.01,0.01
+MapArray,5000,0.81,0.80
+Dictionary,5000,0.02,0.02
+Map,5000,0.01,0.01
+MapArray,10000,1.66,1.66
+Dictionary,10000,0.05,0.04
+Map,10000,0.02,0.02
\ No newline at end of file
diff --git a/bench/churn-sweep.ts b/bench/churn-sweep.ts
new file mode 100644
index 0000000..a34a18a
--- /dev/null
+++ b/bench/churn-sweep.ts
@@ -0,0 +1,89 @@
+// bench/churn-sweep.ts
+import { Bench } from "tinybench";
+import { type Box, box } from "../engine/lib/box.ts";
+import {
+	createDictionary,
+	deleteEntry,
+	setEntry,
+} from "../engine/lib/Dictionary.ts";
+import MapArray from "../engine/lib/MapArray.ts";
+
+const SIZES = [100, 250, 500, 999, 2500, 5000, 10000];
+const CHURN_N = 100;
+const churnKeys = Array.from({ length: CHURN_N }, (_, i) => `churn-${i}`);
+
+let sink = 0;
+
+function makeBaseData(size: number): Array<[string, Box<number>]> {
+	const data: Array<[string, Box<number>]> = [];
+	let i = size;
+	while (i-- > 0) data.push([String(i), box(i)]);
+	return data;
+}
+
+type Row = {
+	structure: string;
+	size: number;
+	latencyNsAvg: number;
+	latencyNsMed: number;
+};
+const rows: Row[] = [];
+
+for (const size of SIZES) {
+	const baseData = makeBaseData(size);
+
+	const ma = new MapArray(structuredClone(baseData));
+	const dict = createDictionary(structuredClone(baseData));
+	const map = new Map(structuredClone(baseData));
+
+	const bench = new Bench({ name: `churn @ size=${size}`, time: 500 });
+
+	bench
+		.add("MapArray", () => {
+			for (const key of churnKeys) ma.set(key, box(1));
+			for (const key of churnKeys) ma.delete(key);
+			sink += ma.entries().length;
+		})
+		.add("Dictionary", () => {
+			for (const key of churnKeys) setEntry(dict, [key, box(1)]);
+			for (const key of churnKeys) deleteEntry(dict, key);
+			sink += dict.entries.length;
+		})
+		.add("Map", () => {
+			for (const key of churnKeys) map.set(key, box(1));
+			for (const key of churnKeys) map.delete(key);
+			sink += map.size;
+		});
+
+	await bench.run();
+
+	for (const task of bench.tasks) {
+		const res = task.result;
+		if (!res) continue;
+		rows.push({
+			structure: task.name,
+			size,
+			latencyNsAvg: res.latency.mean,
+			latencyNsMed: res.latency.p50 ?? res.latency.mean,
+		});
+	}
+
+	console.log(`-- size=${size} done --`);
+	console.table(bench.table());
+}
+
+// CSV output
+const header = "structure,size,latency_ns_avg,latency_ns_med";
+const csvLines = rows.map(
+	(r) =>
+		`${r.structure},${r.size},${r.latencyNsAvg.toFixed(2)},${r.latencyNsMed.toFixed(2)}`,
+);
+const csv = [header, ...csvLines].join("\n");
+
+(await Deno.writeTextFile?.("churn-sweep.csv", csv)) ??
+	(await import("node:fs/promises")).then((fs) =>
+		fs.writeFile("churn-sweep.csv", csv),
+	);
+
+console.log("\nWrote churn-sweep.csv");
+console.log("sink (ignore):", sink);
diff --git a/bench/churn.ts b/bench/churn.ts
new file mode 100644
index 0000000..45f07bc
--- /dev/null
+++ b/bench/churn.ts
@@ -0,0 +1,77 @@
+// bench/churn.ts
+import { Bench } from "tinybench";
+import { type Box, box } from "./../engine/lib/box.ts";
+import {
+	createDictionary,
+	deleteEntry,
+	getEntry,
+	setEntry,
+} from "./../engine/lib/Dictionary.ts";
+import MapArray from "./../engine/lib/MapArray.ts";
+
+const bench = new Bench({ name: "churn", time: 1000 });
+
+const SIZE = 999;
+const baseData: Array<[string, Box<number>]> = [];
+{
+	let i = SIZE;
+	while (i-- > 0) baseData.push([String(i), box(i)]);
+}
+
+// Churn keys: a rotating window of "new" entities not in the base set,
+// so every set/delete pair actually does real insert+remove work
+// rather than repeatedly hitting the same already-resident key.
+const CHURN_N = 100;
+const churnKeys = Array.from({ length: CHURN_N }, (_, i) => `churn-${i}`);
+
+let sink = 0; // anti-DCE: something observable reads this later
+
+function freshMapArray() {
+	return new MapArray(structuredClone(baseData));
+}
+function freshDictionary() {
+	return createDictionary(structuredClone(baseData));
+}
+function freshMap() {
+	return new Map(structuredClone(baseData));
+}
+
+// Each task rebuilds nothing per-iteration except doing insert+remove
+// on a fixed churn window against a persistent SIZE-element base structure —
+// this mirrors "N entities steady-state, M entering/leaving per frame".
+const ma = freshMapArray();
+const dict = freshDictionary();
+const map = freshMap();
+
+bench
+	.add("MapArray churn (set+delete)", () => {
+		for (const key of churnKeys) {
+			ma.set(key, box(1));
+		}
+		for (const key of churnKeys) {
+			ma.delete(key);
+		}
+		sink += ma.entries().length;
+	})
+	.add("Dictionary churn (set+delete)", () => {
+		for (const key of churnKeys) {
+			setEntry(dict, [key, box(1)]);
+		}
+		for (const key of churnKeys) {
+			deleteEntry(dict, key);
+		}
+		sink += dict.entries.length;
+	})
+	.add("Map churn (set+delete)", () => {
+		for (const key of churnKeys) {
+			map.set(key, box(1));
+		}
+		for (const key of churnKeys) {
+			map.delete(key);
+		}
+		sink += map.size;
+	});
+
+await bench.run();
+console.table(bench.table());
+console.log("sink (ignore):", sink);