Bon comme tu avais l’air d’insister 
, j’ai essayé sgfxi sur une Wheezy installée sur une partition séparée du DD.
sgfxi fonctionne mal, il faut utiliser smxi.
Quelle usine à gaz ce script !!! 
Enfin après moultes questions-réponses, ça avait l’air de bien marcher.
J’ai donc tout viré sur ma version de Wheezy, et lancé smxi. Impeccable, le driver 174.14.35 est installé et j’ai acces à la configuration dans nvidia-settings.
Sauf qu’à chaque redémarrage, l’affichage revient sur default et 50 Hz.
Et c’est bien ce que je pensais, il y a quelque chose qui parametre ça, la preuve cet extrait du xorg.0.log:
[quote][ 23.370] (II) LoadModule: “ramdac”
[ 23.370] (II) Module “ramdac” already built-in
[ 23.381] () NVIDIA(0): Depth 24, (–) framebuffer bpp 32
[ 23.381] (==) NVIDIA(0): RGB weight 888
[ 23.382] (==) NVIDIA(0): Default visual is TrueColor
[ 23.382] (==) NVIDIA(0): Using gamma correction (1.0, 1.0, 1.0)
[ 23.382] () NVIDIA(0): Option “TwinView” “0”
[ 23.382] () NVIDIA(0): Option “MetaModes” “1680x1050 +0+0; nvidia-auto-select +0+0”
[ 23.382] () NVIDIA(0): Option “TwinViewXineramaInfoOrder” “CRT-0”
[ 23.390] (**) NVIDIA(0): Enabling RENDER acceleration
[ 23.401] (II) NVIDIA(0): Support for GLX with the Damage and Composite X extensions is
[ 23.401] (II) NVIDIA(0): enabled.
[ 24.094] (II) NVIDIA(0): NVIDIA GPU GeForce FX 5200 (NV34) at PCI:1:0:0 (GPU-0)
[ 24.094] (–) NVIDIA(0): Memory: 65536 kBytes
[ 24.094] (–) NVIDIA(0): VideoBIOS: 04.34.20.87.00
[ 24.094] (II) NVIDIA(0): Detected AGP rate: 8X
[ 24.094] (–) NVIDIA(0): Interlaced video modes are supported on this GPU
[ 24.094] (–) NVIDIA(0): Connected display device(s) on GeForce FX 5200 at PCI:1:0:0:
[ 24.094] (–) NVIDIA(0): Samsung SyncMaster (CRT-0)
[ 24.094] (–) NVIDIA(0): Samsung SyncMaster (CRT-0): 350.0 MHz maximum pixel clock
[ 24.095] (II) NVIDIA(0): Assigned Display Device: CRT-0
[ 24.095] (II) NVIDIA(0): Validated modes:
[ 24.095] (II) NVIDIA(0): “1680x1050+0+0”
[ 24.095] (II) NVIDIA(0): “nvidia-auto-select+0+0”
[ 24.095] (II) NVIDIA(0): Virtual screen size determined to be 1680 x 1050
[ 24.096] (–) NVIDIA(0): DPI set to (90, 88); computed from “UseEdidDpi” X config
[ 24.096] (–) NVIDIA(0): option
[ 24.096] (==) NVIDIA(0): Enabling 32-bit ARGB GLX visuals.
[ 24.096] (–) Depth 24 pixmap format is 32 bpp
[ 24.097] (II) NVIDIA(0): Initialized AGP GART.
[ 24.101] (II) NVIDIA(0): Setting mode “1680x1050+0+0”[/quote]
On voit bien qu’il y a un “nvidia-auto-select” qui parametre le bouzin. Mais où? 
Deuxième chose surprenante: Dans synaptic il n’y aucun nvidia, 173.14.35 ou xserver.xorgxxxx d’installé… 