diff --git a/OpenRA.Game/FileSystem/ZipFile.cs b/OpenRA.Game/FileSystem/ZipFile.cs
index e8ebf9ef0d..f1818aabff 100644
--- a/OpenRA.Game/FileSystem/ZipFile.cs
+++ b/OpenRA.Game/FileSystem/ZipFile.cs
@@ -44,7 +44,7 @@ namespace OpenRA.FileSystem
 
 				using (var z = pkg.GetInputStream(entry))
 				{
-					var ms = new MemoryStream();
+					var ms = new MemoryStream((int)entry.Size);
 					z.CopyTo(ms);
 					ms.Seek(0, SeekOrigin.Begin);
 					return ms;
@@ -104,7 +104,13 @@ namespace OpenRA.FileSystem
 				// SharpZipLib breaks when asked to update archives loaded from outside streams or files
 				// We can work around this by creating a clean in-memory-only file, cutting all outside references
 				if (!create)
-					new MemoryStream(File.ReadAllBytes(filename)).CopyTo(pkgStream);
+				{
+					using (var copy = new MemoryStream(File.ReadAllBytes(filename)))
+					{
+						pkgStream.Capacity = (int)copy.Length;
+						copy.CopyTo(pkgStream);
+					}
+				}
 
 				pkgStream.Position = 0;
 				pkg = ZipFileHelper.Create(pkgStream);
diff --git a/OpenRA.Game/Network/Connection.cs b/OpenRA.Game/Network/Connection.cs
index 66d6c655d9..3db4471fca 100644
--- a/OpenRA.Game/Network/Connection.cs
+++ b/OpenRA.Game/Network/Connection.cs
@@ -77,10 +77,10 @@ namespace OpenRA.Network
 
 		public virtual void SendSync(int frame, byte[] syncData)
 		{
-			var ms = new MemoryStream();
+			var ms = new MemoryStream(4 + syncData.Length);
 			ms.Write(BitConverter.GetBytes(frame));
 			ms.Write(syncData);
-			Send(ms.ToArray());
+			Send(ms.GetBuffer());
 		}
 
 		protected virtual void Send(byte[] packet)
@@ -197,10 +197,10 @@ namespace OpenRA.Network
 
 		public override void SendSync(int frame, byte[] syncData)
 		{
-			var ms = new MemoryStream();
+			var ms = new MemoryStream(4 + syncData.Length);
 			ms.Write(BitConverter.GetBytes(frame));
 			ms.Write(syncData);
-			queuedSyncPackets.Add(ms.ToArray());
+			queuedSyncPackets.Add(ms.GetBuffer());
 		}
 
 		protected override void Send(byte[] packet)
diff --git a/OpenRA.Game/Network/Order.cs b/OpenRA.Game/Network/Order.cs
index 2deb2bff76..68f4684678 100644
--- a/OpenRA.Game/Network/Order.cs
+++ b/OpenRA.Game/Network/Order.cs
@@ -240,7 +240,7 @@ namespace OpenRA
 		{
 			if (IsImmediate)
 			{
-				var ret = new MemoryStream();
+				var ret = new MemoryStream(1 + OrderString.Length + 1 + TargetString.Length + 1);
 				var w = new BinaryWriter(ret);
 				w.Write((byte)0xfe);
 				w.Write(OrderString);
diff --git a/OpenRA.Game/Network/OrderIO.cs b/OpenRA.Game/Network/OrderIO.cs
index 750992a26d..26d0675784 100644
--- a/OpenRA.Game/Network/OrderIO.cs
+++ b/OpenRA.Game/Network/OrderIO.cs
@@ -38,14 +38,14 @@ namespace OpenRA.Network
 
 		public static byte[] SerializeSync(int sync)
 		{
-			var ms = new MemoryStream();
+			var ms = new MemoryStream(1 + 4);
 			using (var writer = new BinaryWriter(ms))
 			{
 				writer.Write((byte)0x65);
 				writer.Write(sync);
 			}
 
-			return ms.ToArray();
+			return ms.GetBuffer();
 		}
 
 		public static int2 ReadInt2(this BinaryReader r)
diff --git a/OpenRA.Game/Network/ReplayConnection.cs b/OpenRA.Game/Network/ReplayConnection.cs
index 2cc2176e26..71dfcf5afd 100644
--- a/OpenRA.Game/Network/ReplayConnection.cs
+++ b/OpenRA.Game/Network/ReplayConnection.cs
@@ -127,10 +127,10 @@ namespace OpenRA.Network
 
 		public void SendSync(int frame, byte[] syncData)
 		{
-			var ms = new MemoryStream();
+			var ms = new MemoryStream(4 + syncData.Length);
 			ms.Write(BitConverter.GetBytes(frame));
 			ms.Write(syncData);
-			sync.Add(ms.ToArray());
+			sync.Add(ms.GetBuffer());
 
 			// Store the current frame so Receive() can return the next chunk of orders.
 			ordersFrame = frame + LobbyInfo.GlobalSettings.OrderLatency;
diff --git a/OpenRA.Game/Server/ServerOrder.cs b/OpenRA.Game/Server/ServerOrder.cs
index 0ecbcfa3cf..818e6b19de 100644
--- a/OpenRA.Game/Server/ServerOrder.cs
+++ b/OpenRA.Game/Server/ServerOrder.cs
@@ -49,7 +49,7 @@ namespace OpenRA.Server
 
 		public byte[] Serialize()
 		{
-			var ms = new MemoryStream();
+			var ms = new MemoryStream(1 + Name.Length + 1 + Data.Length + 1);
 			var bw = new BinaryWriter(ms);
 
 			bw.Write((byte)0xfe);
diff --git a/OpenRA.Mods.Cnc/FileSystem/MixFile.cs b/OpenRA.Mods.Cnc/FileSystem/MixFile.cs
index 3fab1ccb94..77508d5ef6 100644
--- a/OpenRA.Mods.Cnc/FileSystem/MixFile.cs
+++ b/OpenRA.Mods.Cnc/FileSystem/MixFile.cs
@@ -150,7 +150,7 @@ namespace OpenRA.Mods.Cnc.FileSystem
 			{
 				var decrypted = fish.Decrypt(h);
 
-				var ms = new MemoryStream();
+				var ms = new MemoryStream(decrypted.Length * 4);
 				var writer = new BinaryWriter(ms);
 				foreach (var t in decrypted)
 					writer.Write(t);