Very naïve approach.
Tcl, 109 bytes
set i 0;time {puts [format %$i.s \ ][string repe [format %c [expr $i+65]]\ [incr i]]} [expr [scan $c %c]-64]
set i 0;time {puts [string repe \ $i][string repe [format %c [expr $i+65]]\ [incr i]]} [expr [scan $c %c]-64]