Насколько медленны iostreams?

Что произойдёт, если я всё же включу её перед считыванием данных из файла?

#include <stdio.h>

long read_batched(long *out)
{
    char buf[20];
    long c, x = 0, neg = 0;
    char *res = fgets(buf, sizeof(buf), stdin);
    if (res == NULL) return 0;

    while ((c = *(res++)) != 0) {
        if ('0' <= c && c <= '9') {
            x = x*10 + c - '0';
        } else if (c == '-') {
            neg = 1;
        } else {
            break;
        }
    }

    *out = neg ? -x : x;
    return 1;
}

int main()
{
    long x;
    long max = -1;

    while (read_batched(&x)) {
	    if (x > max) max = x;
    }
    printf("%ld\n", max);
    return 0;
}

package readnum;

import java.util.Scanner;

public class ReadNum {
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		double max = 0;
		while (sc.hasNextDouble()) {
			double next = sc.nextDouble();
			if (next > max) {
				max = next;
			}
		}
		sc.close();
		System.out.println("Max: " + max);
	}
}

$ time java -cp bin readnum.ReadNum < data
Max: 1.0E7

real    1m2.414s
user    0m0.015s
sys     0m0.031s

package readnum;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Scanner;

public class ReadNum {
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		double max = 0;
		while (sc.hasNextDouble()) {
			double next = sc.nextDouble();
			if (next > max) {
				max = next;
			}
		}
		sc.close();
		System.out.println("Max: " + max);
	}
}

$ time java -cp bin readnum.ReadNum < data
Max: 1.0E7

real    1m1.802s
user    0m0.015s
sys     0m0.015s

package readnum;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class ReadNum {
	public static void main(String[] args) throws IOException {
		
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		double max = 0;
		String line;
		while ((line = br.readLine()) != null) {
			double next = Double.parseDouble(line);
			if (next > max) {
				max = next;
			}
		}
		br.close();
		System.out.println("Max: " + max);
	}
}

$ time java -cp bin readnum.ReadNum < data
Max: 1.0E7

real    0m2.222s
user    0m0.000s
sys     0m0.047s

import qualified Data.ByteString.Lazy.Char8 as B
import Data.Maybe
import Data.List

main = B.interact $ B.pack . show . foldl' max 0 . map (fst . fromJust . B.readInt) . B.lines