speed comparison between fgetc/fputc and fread/fwrite in C

So(just for fun), i was just trying to write a C code to copy a file. I read around and it seems that all the functions to read from a stream call fgetc() (I hope this is this true?), so I used that function:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define FILEr "img1.png"
#define FILEw "img2.png"
main()
{
    clock_t start,diff;
    int msec;
    FILE *fr,*fw;
    fr=fopen(FILEr,"r");
    fw=fopen(FILEw,"w");
    start=clock();
    while((!feof(fr)))
        fputc(fgetc(fr),fw);
    diff=clock()-start;
    msec=diff*1000/CLOCKS_PER_SEC;
    printf("Time taken %d seconds %d milliseconds\n", msec/1000, msec%1000);
    fclose(fr);
    fclose(fw);
}

This gave a run time of 140 ms for this file on a 2.10Ghz core2Duo T6500 Dell inspiron laptop. However, when I try using fread/fwrite, I get decreasing run time as I keep increasing the number of bytes(ie. variable st in the following code) transferred for each call until it peaks at around 10ms! Here is the code:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define FILEr "img1.png"
#define FILEw "img2.png"
main()
{
    clock_t start,diff;
    // number of bytes copied at each step
    size_t st=10000;
    int msec;
    FILE *fr,*fw;
    // placeholder for value that is read
    char *x;
    x=malloc(st);
    fr=fopen(FILEr,"r");
    fw=fopen(FILEw,"w");
    start=clock();
    while(!feof(fr))
     {
        fread(x,1,st,fr);
        fwrite(x,1,st,fw);
     }
    diff=clock()-start;
    msec=diff*1000/CLOCKS_PER_SEC;
    printf("Time taken %d seconds %d milliseconds\n", msec/1000, msec%1000);
    fclose(fr);
    fclose(fw);
    free(x);
}

Why this is happening? I.e if fread i