Since all of your versions of log-factorial show roughly similar run-times,
I'll concentrate on LOG-FACTORIAL-C.  Timings are on a SparcStation 1+, 20mhz
clock, 24meg memory.

With CMU Common Lisp 16e:
    common-lisp-user> (time (log-factorial-c 10000))
    Evaluation took:
      0.43 seconds of real time
      0.4 seconds of user run time
      0.03 seconds of system run time
      0 page faults and
      160000 bytes consed.
    82108.95

With Franz Allegro "4.0.1 [Sun4] (2/8/91)":
    <cl> (time (log-factorial-c 10000))
    cpu time (non-gc) 1984 msec user, 367 msec system
    cpu time (gc)     533 msec user, 150 msec system
    cpu time (total)  2517 msec user, 517 msec system
    real time  3538 msec
    space allocation:
     2 cons cells, 0 symbols, 1280016 other bytes,
    82108.95 


I wrote a modified version of LOG-FACTORIAL-C with declarations that are more
to CMU CL's liking:
    (defun log-factorial-cmu (n)
      "Calculates log of n-factorial non-recursively."
      (declare (fixnum n))
      (let ((result 0.0))
	(declare (single-float result))
	(do ((i 1 (1+ i)))
	    ((> i n) result)
	  (declare (fixnum i))
	  (incf result (the single-float (log (coerce i 'single-float)))))))

With CMU Common Lisp 16e:
    common-lisp-user> (time (log-factorial-cmu 10000))
    Evaluation took:
      0.23 seconds of real time
      0.23 seconds of user run time
      0.0 seconds of system run time
      0 page faults and
      8 bytes consed.
    82108.95
 
With Franz Allegro "4.0.1 [Sun4] (2/8/91)":
    <cl> (time (log-factorial-cmu 10000))
    cpu time (non-gc) 3383 msec user, 317 msec system
    cpu time (gc)     567 msec user, 0 msec system
    cpu time (total)  3950 msec user, 317 msec system
    real time  4363 msec
    space allocation:
     2 cons cells, 0 symbols, 1600016 other bytes,
    82108.95 



<cl> (time (log-factorial-a 10000))
(time (log-factorial-c 10000))
(time (log-factorial-d 10000))
(time (log-factorial-e 10000))
(time (log-factorial-f 10000))
(time (log-factorial-cmu 10000))
cpu time (non-gc) 2166 msec user, 284 msec system
cpu time (gc)     8100 msec user, 66 msec system
cpu time (total)  10266 msec user, 350 msec system
real time  10634 msec
space allocation:
 2 cons cells, 0 symbols, 1280016 other bytes,
82108.95 
<cl> cpu time (non-gc) 2016 msec user, 66 msec system
cpu time (gc)     517 msec user, 17 msec system
cpu time (total)  2533 msec user, 83 msec system
real time  2671 msec
space allocation:
 2 cons cells, 0 symbols, 1280016 other bytes,
82108.95 
<cl> cpu time (non-gc) 2016 msec user, 0 msec system
cpu time (gc)     517 msec user, 17 msec system
cpu time (total)  2533 msec user, 17 msec system
real time  2538 msec
space allocation:
 2 cons cells, 0 symbols, 1280016 other bytes,
82108.95 
<cl> cpu time (non-gc) 1934 msec user, 16 msec system
cpu time (gc)     516 msec user, 0 msec system
cpu time (total)  2450 msec user, 16 msec system
real time  2468 msec
space allocation:
 2 cons cells, 0 symbols, 1280016 other bytes,
82108.95 
<cl> cpu time (non-gc) 1933 msec user, 0 msec system
cpu time (gc)     534 msec user, 0 msec system
cpu time (total)  2467 msec user, 0 msec system
real time  2469 msec
space allocation:
 2 cons cells, 0 symbols, 1280016 other bytes,
82108.95 
<cl> cpu time (non-gc) 2434 msec user, 33 msec system
cpu time (gc)     516 msec user, 0 msec system
cpu time (total)  2950 msec user, 33 msec system
real time  2996 msec
space allocation:
 2 cons cells, 0 symbols, 1600032 other bytes,
82108.95 
<cl> 

;;;; Same machine, CMU Common Lisp 16e

common-lisp-user> (time (log-factorial-a 10000))
(time (log-factorial-c 10000))
(time (log-factorial-d 10000))
(time (log-factorial-e 10000))
(time (log-factorial-f 10000))
(time (log-factorial-cmu 10000))
Compiling LAMBDA NIL: 
Compiling Top-Level Form: 

Evaluation took:
  0.47 seconds of real time
  0.46 seconds of user run time
  0.01 seconds of system run time
  0 page faults and
  160000 bytes consed.
82108.95
common-lisp-user> Compiling LAMBDA NIL: 
Compiling Top-Level Form: 

Evaluation took:
  0.43 seconds of real time
  0.4 seconds of user run time
  0.03 seconds of system run time
  0 page faults and
  160000 bytes consed.
82108.95
common-lisp-user> Compiling LAMBDA NIL: 
Compiling Top-Level Form: 

Evaluation took:
  0.47 seconds of real time
  0.44 seconds of user run time
  0.03 seconds of system run time
  0 page faults and
  160000 bytes consed.
82108.95
common-lisp-user> Compiling LAMBDA NIL: 
Compiling Top-Level Form: 

Evaluation took:
  0.42 seconds of real time
  0.4 seconds of user run time
  0.02 seconds of system run time
  0 page faults and
  160000 bytes consed.
82108.95
common-lisp-user> Compiling LAMBDA NIL: 
Compiling Top-Level Form: 

Evaluation took:
  0.43 seconds of real time
  0.4 seconds of user run time
  0.03 seconds of system run time
  0 page faults and
  160000 bytes consed.
82108.95
common-lisp-user> Compiling LAMBDA NIL: 
Compiling Top-Level Form: 
[GC threshold exceeded with 1,138,712 bytes in use.  Commencing GC.]
[GC completed with 141,904 bytes retained and 996,808 bytes freed.]
[GC will next occur when at least 1,141,904 bytes are in use.]

Evaluation took:
  0.23 seconds of real time
  0.23 seconds of user run time
  0.0 seconds of system run time
  0 page faults and
  8 bytes consed.
82108.95
common-lisp-user>