awk 'NR==FNR{a[NR]=$0;next} {print a[FNR] "t",$5}' file1 file2

set -- file*
fields="-f-5,$(seq -s, 10 5 $((5*$#)))"
paste "$@" | cut ${fields%?} >outfile

awk -F "t" '
    { key = $1 FS $2 FS $3 FS $4; values[key] = values[key] FS $5 }
    END { for (key in values) print key values[key] }
' file ...

awk -F "t" '
    BEGIN { header = "col1" FS "col2" FS "col3" FS "col4" }
    {
        key = $1 FS $2 FS $3 FS $4
        values[key] = values[key] FS $5
    }
    FNR == 1 {
        split(FILENAME, a, /_/)
        header = header FS a[2]
    }
    END {
        print header
        for (key in values)
            print key values[key]
    }
' file ...

END {
        print header
        # order the array by index, as strings, ascending
        PROCINFO["sorted_in"] = "@ind_str_asc"
        for (key in values)
            print key values[key]
    }

awk '...' | {
    read header
    echo "$header"
    sort
}