diff --git a/PKHeX.Core/Saves/MemeCrypto/MemeCrypto.cs b/PKHeX.Core/Saves/MemeCrypto/MemeCrypto.cs
index 94e60f244..8dbe36707 100644
--- a/PKHeX.Core/Saves/MemeCrypto/MemeCrypto.cs
+++ b/PKHeX.Core/Saves/MemeCrypto/MemeCrypto.cs
@@ -7,7 +7,7 @@ namespace PKHeX.Core
     /// MemeCrypto V1 - The Original Series
     /// </summary>
     /// <remarks>
-    /// A variant of <see cref="SaveFile"/> encryption and obfuscation, used in <see cref="GameVersion.Gen7"/>.
+    /// A variant of <see cref="SaveFile"/> encryption and obfuscation used in <see cref="GameVersion.Gen7"/>.
     /// <br> The save file stores a dedicated block to contain a hash of the savedata, computed when the block is zeroed. </br>
     /// <br> This signing logic is reused for other authentication; refer to <see cref="MemeKeyIndex"/>. </br>
     /// <br> The save file first computes a SHA256 Hash over the block checksum region.
diff --git a/PKHeX.Core/Saves/MemeCrypto/SwishCrypto.cs b/PKHeX.Core/Saves/MemeCrypto/SwishCrypto.cs
index dd5c37011..d6125aa11 100644
--- a/PKHeX.Core/Saves/MemeCrypto/SwishCrypto.cs
+++ b/PKHeX.Core/Saves/MemeCrypto/SwishCrypto.cs
@@ -111,9 +111,12 @@ public static byte[] GetDecryptedRawData(byte[] data)
             return temp;
         }
 
+        private const int BlockDataRatioEstimate1 = 777; // bytes per block, on average (generous)
+        private const int BlockDataRatioEstimate2 = 555; // bytes per block, on average (stingy)
+
         private static IReadOnlyList<SCBlock> ReadBlocks(byte[] data)
         {
-            var result = new List<SCBlock>();
+            var result = new List<SCBlock>(data.Length / BlockDataRatioEstimate2);
             int offset = 0;
             while (offset < data.Length - SIZE_HASH)
             {
@@ -144,9 +147,9 @@ public static byte[] Encrypt(IReadOnlyList<SCBlock> blocks)
         /// Tries to encrypt the save data.
         /// </summary>
         /// <returns>Raw save data without the final xorpad layer.</returns>
-        public static byte[] GetDecryptedRawData(IEnumerable<SCBlock> blocks)
+        public static byte[] GetDecryptedRawData(IReadOnlyList<SCBlock> blocks)
         {
-            using var ms = new MemoryStream();
+            using var ms = new MemoryStream(blocks.Count * BlockDataRatioEstimate1);
             using var bw = new BinaryWriter(ms);
             foreach (var block in blocks)
                 block.WriteBlock(bw);