# cat file1
111     222     ABC     PQR     0.1
333     444     xxx     yyy     0.5
555     666     PQR     DEF     0.4
 
# cat file2
111     222     abc     xyz     0.7
555     666     def     pqr     0.3
777     888     rst     mno     0.4

# ./justdoit
111     222     abc     xyz     0.7
555     666     PQR     DEF     0.4

## justdoit ##
#!/bin/bash
cnt=$(sed -n '$=' file1) ; cntx=$(sed -n '$=' file2)
if [[ $cnt -gt $cntx ]] ; then
  count=$cntx
 else
  count=$cnt
fi
rm -f justtmp
x=1
while [ $(( count -= 1 )) -gt -1 ]
 do
  a=$(sed -n "$x s/^\([^\t]*\)\t\([^\t]*\).*/\1 \2/p" file1)  # first and second tab chars
  for i in $(seq 1 3)
   do
    a1=$(sed -n "$i s/^\([^\t]*\)\t\([^\t]*\).*/\1 \2/p" file2)
    if [[ $a == $a1 ]] ; then
      line1=$(echo " `sed -n "$x s/.*\t\(.*\)$/\1/p" file1` * 1000" | bc | sed 's/\..*//')
      line2=$(echo " `sed -n "$i s/.*\t\(.*\)$/\1/p" file2` * 1000" | bc | sed 's/\..*//')
       if [[ $line1 -lt $line2 ]] ; then
        sed -n "$x s/^\([^\t]*\)\t\([^\t]*\).*/\1\t\2/p" file1 > tmpx
        sed -n "$i s/^[^\t]*\t[^\t]*\t//p" file2 > tmpX
        paste -d"\t" tmpx tmpX >> justtmp
       else
        sed -n "$i s/^\([^\t]*\)\t\([^\t]*\).*/\1\t\2/p" file2 > tmpx
        sed -n "$x s/^[^\t]*\t[^\t]*\t//p" file1 > tmpX
        paste -d"\t" tmpx tmpX >> justtmp
       fi
    fi
   done
   let x=$x+1
 done
more justtmp