lsearch slowdown

package require fileutil

#     Benchmark showing the impact on lsearch in Tcl 8.6.11
#
#     $ fossil info 26e57ca1486e497b
#     hash:         26e57ca1486e497b32e75a074c0ee81b62beefb8 2020-05-05 16:00:06 UTC
#     parent:       5d38a6b3c64572f808163ae7656333fea1e478a7 2020-05-05 15:56:14 UTC
#     child:        b275de7c6434b50adf9f27ff24d01bd972efa624 2020-05-06 08:15:49 UTC
#     merged-into:  b07935f03d33d1bdfb89a4b13f1fee914d78080d 2020-05-05 16:20:24 UTC
#     tags:         core-8-6-branch
#     comment:      More usage of TclUtfToUCS4(), so we can use the whole Unicode range better in TCL_UTF_MAX>3 builds. (user: jan.nijtmans)

#
#     $ /usr/local/tcl8.6.11/bin/tclsh8.6 lbench.tcl 
#     stringlist has 5000 items.
#     lsearch returned -1 took 2297 microseconds.
#     lsearch -exact returned -1 took 23 microseconds.
#     $ /usr/local/tcl8.6.10/bin/tclsh8.6 lbench.tcl 
#     stringlist has 5000 items.
#     lsearch returned -1 took 512 microseconds.
#     lsearch -exact returned -1 took 24 microseconds.
#
# 

set alphabet [ list X M R 0 1 2 3 4 5 6 7 8 9 / ]

# based on suchenwi's random string generator from the Tcl Wiki:
proc lpick L {lindex $L [expr {int(rand()*[llength $L])}]}
proc randomlyPicked { length {chars { X 0 1 2 3 4 5 6 7 8 9 / }} } {
    for {set i 0} {$i<$length} {incr i} {append res [lpick $chars]}
    return $res
}

set stringlist [ list ]

# Generate some repetitive random strings
# Start all strings with a common prefix
set string_prefix "X14/X33/X5/X1848/X1/X3/X1/X1/X1/X1/X8/X49/X34"

set numstrings 5000

for { set n 0 } { $n < $numstrings } { incr n } {
    set random_length [ expr { 5 + int(rand()*25) } ]
    set new_string "$string_prefix/[ randomlyPicked $random_length ]"
    lappend stringlist $new_string
}

# Search for a unique string that also has the same common prefix
set search_for "$string_prefix/M0"
puts "stringlist has [ llength $stringlist ] items."

set timer [ clock microseconds ]

set finder [ lsearch $stringlist $search_for ]

puts "lsearch returned $finder took [ expr { [ clock microseconds ] - $timer } ] microseconds."

set timer [ clock microseconds ]

set finder [ lsearch -exact $stringlist $search_for ]

puts "lsearch -exact returned $finder took [ expr { [ clock microseconds ] - $timer } ] microseconds."