Lisp/Genera advantages over C (plea for help)

[GODDEN%gmr.com@RELAY.CS.NET]

I am preaching for the use of Common Lisp/CLOS in a new project here,
while every one else in the group prefers C.  The reasons for C are:
1. runs on UNIX boxes
2. is portable
3. offers better performance than Lisp.

I am claiming that CL satisfies both 1 and 2; and I'm rejecting 3
altogether.  I'm basing that rejection on statements such as at the
bottom of p.2 in CLtL (to wit: there are Lisp compilers that produce
numerical code on a par with Fortran compilers), and there are
known techniques for optimizing Lisp programs and compilers (e.g. 
use of macros, avoidance of consing, tail-recursion optimizations).  

A counter-argument I have just encountered is the observation that
some (many) AI vendors have converted their code from Lisp to C
'for performance'.  My response is that such moves constitue wise
marketing because MIS managers have never heard of Lisp, or have
heard that it's a performance dog.  Rather than fight the world,
the vendors figure it's easier to give them what they want (C),
and tell them what they want to hear (Lisp is a dog).  Perhaps
I'm wrong, and the vendors provide C for sound technical reasons.
Can anyone enlighten me further on this point (i.e. give me some
ammo).  Naturally, my most significant argument is that CL and
Genera will offer us superior productivity.  But that is one issue
of several, and I need to meet the opposition on their own turf.
-Kurt Godden
 godden@gmr.com