J'ai essayer de booter sans ram ... la carte aime pas.
J'ai donc testé avec une barrette de 256mo , ça passe même si seulement 128mo sont détecté.
Sous vista avec hdtune ,ça n'a pas l'air de changer grand chose :
 
Sous linux avec bonnie++ , ça n'as pas bougé d'un poil :
[cpp]Version 1.03c       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
Phangos          1G 13248  89 16793  27  7355  10 14654  81 17694  15 191.0   1
                    ------Sequential Create------ --------Random Create--------
                    -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 10   519   4 +++++ +++   487   3   532   5 +++++ +++   489   4
Phangos,1G,13248,89,16793,27,7355,10,14654,81,17694,15,191.0,1,10,519,4,+++++,+++,487,3,532,5,+++++,+++,489,4
[/cpp]
Par contre hdparm me fait des trucs bizzard : 
[cpp]/dev/sda:
 Timing cached reads:   302 MB in  2.01 seconds = 150.03 MB/sec
 Timing buffered disk reads:   64 MB in  3.10 seconds =  20.66 MB/sec
/dev/sda:
 Timing cached reads:   294 MB in  2.01 seconds = 146.41 MB/sec
 Timing buffered disk reads:   72 MB in  3.04 seconds =  23.66 MB/sec
/dev/sda:
 Timing cached reads:   310 MB in  2.01 seconds = 154.33 MB/sec
 Timing buffered disk reads:  104 MB in  3.09 seconds =  33.61 MB/sec
/dev/sda:
 Timing cached reads:   308 MB in  2.01 seconds = 153.50 MB/sec
 Timing buffered disk reads:  112 MB in  3.03 seconds =  36.97 MB/sec
/dev/sda:
 Timing cached reads:   310 MB in  2.01 seconds = 154.14 MB/sec
 Timing buffered disk reads:  130 MB in  3.10 seconds =  41.98 MB/sec
/dev/sda:
 Timing cached reads:   284 MB in  2.01 seconds = 141.30 MB/sec
 Timing buffered disk reads:   66 MB in  3.09 seconds =  21.38 MB/sec
/dev/sda:
 Timing cached reads:   308 MB in  2.00 seconds = 153.68 MB/sec
 Timing buffered disk reads:   72 MB in  3.06 seconds =  23.51 MB/sec
/dev/sda:
 Timing cached reads:   308 MB in  2.01 seconds = 153.11 MB/sec
 Timing buffered disk reads:  104 MB in  3.01 seconds =  34.52 MB/sec
/dev/sda:
 Timing cached reads:   310 MB in  2.01 seconds = 154.24 MB/sec
 Timing buffered disk reads:  112 MB in  3.03 seconds =  36.99 MB/sec
/dev/sda:
 Timing cached reads:   308 MB in  2.01 seconds = 153.26 MB/sec
 Timing buffered disk reads:  128 MB in  3.01 seconds =  42.52 MB/sec
/dev/sda:
 Timing cached reads:   274 MB in  2.00 seconds = 137.00 MB/sec
 Timing buffered disk reads:   66 MB in  3.08 seconds =  21.42 MB/sec
[/cpp]
c'est totalement reproductible ... je l'ai fait 10fois pour être sur , la séquence est toujours la même ...
paradoxalement sur le raid ATA j'ai toujours un résultat de 51Mo/s avec ~1Mo/s de variation :
[cpp]/dev/disk/by-uuid/D008718908716F7A:
 Timing cached reads:   322 MB in  2.01 seconds = 160.50 MB/sec
 Timing buffered disk reads:  156 MB in  3.02 seconds =  51.67 MB/sec
alucard@Phangos:~$ sudo hdparm -tT /dev/disk/by-uuid/D008718908716F7A
[/cpp]
Bon , si les valeurs d'hdparm sont vrai , il y a un peu de mieux ... mais c'est bizzard qu'il y ai autant de variation, une idée de la raison ?