[Leica] M6 metering question

[Simon Lamb <s_lamb@compuserve.com>]

Hi

I have been using my M6 for a few days now and I have a question.  I
pointed the camera at a whitewashed textured wall, with ISO 400 Tri-X
loaded, a 50mm f/2 attached and with the film speed dial set to 400, and
the red dot appeared when the camera was set to a shutter speed of
1000/sec at f/13 or f/14 (whatever the half stop between f/11 and f/16
is on the lens).  I pointed my Nikon F5 at the same spot on the same
wall using an ISO 400 speed and an 85mm f/1.8 lens and, using spot
metering (therefore switching off any colour metering capability), it
registered settings of 400/sec at f/10.

There is a significant difference here and I wondered if anyone could
explain to me the reasons for the difference in metering and subsequent
camera set-up.  I have always trsuted the F5 meter and it has never been
anything other than spot on.  I am sure the M6 meter is equally
accurate.  However, given that I would probably want to dial in some
overexposure on the white wall to get the whiteness and texture on the
film, I do not have any f/stops or shutter speed left to enable me to
overexpose by 1 or 1.5 stops.

Any explanations would be gratefully received.

Regards.

Simon