marvin@smokie:~/perltest $ perl hash_key_bench.pl 
===================================
Latin-1 hash key:
----------------------------------
SV = RV(0x8503ac) at 0x8503a0
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x84df80
  SV = PVHV(0x809048) at 0x84df80
    REFCNT = 2
    FLAGS = (PADMY,SHAREKEYS)
    ARRAY = 0x200f60  (0:7, 1:1)
    hash quality = 100.0%
    KEYS = 1
    FILL = 1
    MAX = 7
    RITER = -1
    EITER = 0x0
    Elt "foo" HASH = 0x238678dd
    SV = IV(0x85036c) at 0x850370
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 1
===================================
UTF-8 hash key:
-----------------------------------
SV = RV(0x8503ac) at 0x8503a0
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x84df40
  SV = PVHV(0x80905c) at 0x84df40
    REFCNT = 2
    FLAGS = (PADMY,SHAREKEYS,HASKFLAGS)
    ARRAY = 0x200f80  (0:7, 1:1)
    hash quality = 100.0%
    KEYS = 1
    FILL = 1
    MAX = 7
    RITER = -1
    EITER = 0x0
    Elt "foo" [UTF8 "foo"] HASH = 0x238678dd
    SV = IV(0x85038c) at 0x850390
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 1
===================================
Results:
-----------------------------------
10 trials of Latin-1 hash key, Latin-1 probe (2.272s total), 227.159ms/trial
10 trials of Latin-1 hash key, UTF-8 probe (2.248s total), 224.823ms/trial
10 trials of UTF-8 hash key, Latin-1 probe (3.100s total), 309.985ms/trial
10 trials of UTF-8 hash key, UTF-8 probe (1.893s total), 189.301ms/trial