Sub-processes cost time in shell scripts - try using a case instead of the multiple if [...] statements - case is a built-in and is thus far faster than the sub-processes necessary to execute if [...].

Maybe something (untested) along the lines of...

>$1.out
unset stat int cpu scpu

echo "Starting rebuild of $1 into $1.out"

while read line ; do
    case $line in
        END)
            cpu=`expr $cpu / 60`

            # Write data line
            echo "$int,$cpu" >>$1.out
            unset stat int cpu scpu
            rec=`expr $rec + 1`
            echo "`date`:Wrote record: $rec"
            ;;
        *GMT | \
        *SAST)
            int=`echo $line|cut -c12-16`
            ;;
        vmstat\ 2\ 60:)
            stat=1
            ;;
        procs |\
        avm)
            :
            ;;
        *)  
            scpu=`echo $line | awk '{ print $16 "+" $17 }'|bc`
            cpu=`expr $cpu + $scpu`
            ;;
    esac
done < $1

echo "Complete!"
[download]

HTH ,