diff --git a/v2/bench_test.go b/v2/bench_test.go
index 16ae9337839bb63bc622724017184ce7fe28bac1..15ae0c24fa0d137fe21987be51c275565765a794 100644
--- a/v2/bench_test.go
+++ b/v2/bench_test.go
@@ -14,8 +14,6 @@ import (
 	carv2 "github.com/ipld/go-car/v2"
 )
 
-var rng = rand.New(rand.NewSource(1413))
-
 // BenchmarkReadBlocks instantiates a BlockReader, and iterates over all blocks.
 // It essentially looks at the contents of any CARv1 or CARv2 file.
 // Note that this also uses internal carv1.ReadHeader underneath.
@@ -59,7 +57,7 @@ func BenchmarkReadBlocks(b *testing.B) {
 // BenchmarkExtractV1File extracts inner CARv1 payload from a sample CARv2 file using ExtractV1File.
 func BenchmarkExtractV1File(b *testing.B) {
 	path := filepath.Join(b.TempDir(), "bench-large-v2.car")
-	generateRandomCarV2File(b, path, 10*1024*1024) // 10 MiB
+	generateRandomCarV2File(b, path, 10<<20) // 10 MiB
 	defer os.Remove(path)
 
 	info, err := os.Stat(path)
@@ -87,7 +85,7 @@ func BenchmarkExtractV1File(b *testing.B) {
 // BenchmarkExtractV1File.
 func BenchmarkExtractV1UsingReader(b *testing.B) {
 	path := filepath.Join(b.TempDir(), "bench-large-v2.car")
-	generateRandomCarV2File(b, path, 10*1024*1024) // 10 MiB
+	generateRandomCarV2File(b, path, 10<<20) // 10 MiB
 	defer os.Remove(path)
 
 	info, err := os.Stat(path)
@@ -121,6 +119,8 @@ func BenchmarkExtractV1UsingReader(b *testing.B) {
 }
 
 func generateRandomCarV2File(b *testing.B, path string, minTotalBlockSize int) {
+	// Use fixed RNG for determinism across benchmarks.
+	rng := rand.New(rand.NewSource(1413))
 	bs, err := blockstore.OpenReadWrite(path, []cid.Cid{})
 	defer func() {
 		if err := bs.Finalize(); err != nil {
@@ -130,7 +130,7 @@ func generateRandomCarV2File(b *testing.B, path string, minTotalBlockSize int) {
 	if err != nil {
 		b.Fatal(err)
 	}
-	buf := make([]byte, 1024)
+	buf := make([]byte, 32<<10) // 32 KiB
 	var totalBlockSize int
 	for totalBlockSize < minTotalBlockSize {
 		size, err := rng.Read(buf)
diff --git a/v2/writer.go b/v2/writer.go
index 91b5340163554e6dc3cf4199e77f81c2b873c082..c344828159039861e624a816329fa783b3704b2e 100644
--- a/v2/writer.go
+++ b/v2/writer.go
@@ -92,6 +92,12 @@ func WrapV1(src io.ReadSeeker, dst io.Writer) error {
 // Note that the destination path might still be created even if an error
 // occurred.
 // If srcPath and dstPath are the same, then the dstPath is converted, in-place, to CARv1.
+//
+// This function aims to extract the CARv1 payload as efficiently as possible.
+// The method is best-effort and depends on your operating system;
+// for example, it should use copy_file_range on recent Linux versions.
+// This API should be preferred over copying directly via Reader.DataReader,
+// as it should allow for better performance while always being at least as efficient.
 func ExtractV1File(srcPath, dstPath string) (err error) {
 	src, err := os.Open(srcPath)
 	if err != nil {
@@ -110,7 +116,7 @@ func ExtractV1File(srcPath, dstPath string) (err error) {
 		return ErrAlreadyV1
 	}
 	if version != 2 {
-		return fmt.Errorf("invalid source version: %v", version)
+		return fmt.Errorf("source version must be 2; got: %d", version)
 	}
 
 	// Read CARv2 header to locate data payload.
@@ -123,11 +129,11 @@ func ExtractV1File(srcPath, dstPath string) (err error) {
 	// Validate header
 	dataOffset := int64(v2h.DataOffset)
 	if dataOffset < PragmaSize+HeaderSize {
-		return fmt.Errorf("invalid data payload offset: %v", dataOffset)
+		return fmt.Errorf("invalid data payload offset: %d", dataOffset)
 	}
 	dataSize := int64(v2h.DataSize)
 	if dataSize <= 0 {
-		return fmt.Errorf("invalid data payload size: %v", dataSize)
+		return fmt.Errorf("invalid data payload size: %d", dataSize)
 	}
 
 	// Seek to the point where the data payload starts
@@ -163,7 +169,7 @@ func ExtractV1File(srcPath, dstPath string) (err error) {
 		return err
 	}
 	if written != dataSize {
-		return fmt.Errorf("expected to write exactly %v but wrote %v", dataSize, written)
+		return fmt.Errorf("expected to write exactly %d but wrote %d", dataSize, written)
 	}
 
 	// Check that the size destination file matches expected size.
diff --git a/v2/writer_test.go b/v2/writer_test.go
index c35beb4a425bbc6a5fa9184320c2d2fa5d2b69b3..c29b43397344510afbe7684b56c491356fad6d05 100644
--- a/v2/writer_test.go
+++ b/v2/writer_test.go
@@ -93,7 +93,7 @@ func TestExtractV1(t *testing.T) {
 func TestExtractV1WithUnknownVersionIsError(t *testing.T) {
 	dstPath := filepath.Join(t.TempDir(), "extract-dst-file-test-v42.car")
 	err := ExtractV1File("testdata/sample-rootless-v42.car", dstPath)
-	require.EqualError(t, err, "invalid source version: 42")
+	require.EqualError(t, err, "source version must be 2; got: 42")
 }
 
 func TestExtractV1FromACarV1IsError(t *testing.T) {