Usability Test Metrics

I've been out of the usability/user centred design field for a few years,
but now am preparing a usability test for an early version of a product that
my company is developing.  I'm considering whether or not to use metrics (ie
user effectiveness, efficiency, etc).  Last time I ran a usability test, the
feeling on metrics seemed to be that they were useful for comparing against
usability targets or different versions of the same system.  I'm not certain
that this benefit will convince my company to spend the extra money required
to produce metrics.  My feeling is the cost-benefit argument is stronger for
a usability test without metrics but with a subjective assessment of user
satisfaction (such as the SUMI questionnaire).  Any opinions on the
usefulness of metrics, for instance to compare different versions of a
product?
Thanks
Lynne



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