while true; do time GUIX_PROFILING=gc ./the-unoptimised-baseN-guix/bin/guix build -d pigx --no-grafts; done

# First run removed
/gnu/store/fq6x8d2vcm6sbjkimg7g8kcgb4c5xv1b-pigx-0.0.3.drv
Garbage collection statistics:
  heap size:        93.85 MiB
  allocated:        325.20 MiB
  GC times:         18
  time spent in GC: 3.69 seconds (24% of user time)

real	0m15,066s
user	0m15,149s
sys	0m0,709s
/gnu/store/fq6x8d2vcm6sbjkimg7g8kcgb4c5xv1b-pigx-0.0.3.drv
Garbage collection statistics:
  heap size:        93.85 MiB
  allocated:        325.19 MiB
  GC times:         18
  time spent in GC: 3.70 seconds (24% of user time)

real	0m15,924s
user	0m15,695s
sys	0m0,836s
/gnu/store/fq6x8d2vcm6sbjkimg7g8kcgb4c5xv1b-pigx-0.0.3.drv
Garbage collection statistics:
  heap size:        93.85 MiB
  allocated:        325.20 MiB
  GC times:         18
  time spent in GC: 3.66 seconds (24% of user time)

real	0m15,369s
user	0m15,339s
sys	0m0,704s
/gnu/store/fq6x8d2vcm6sbjkimg7g8kcgb4c5xv1b-pigx-0.0.3.drv
Garbage collection statistics:
  heap size:        93.85 MiB
  allocated:        325.20 MiB
  GC times:         18
  time spent in GC: 3.69 seconds (25% of user time)

real	0m14,889s
user	0m15,066s
sys	0m0,679s

Summary.

(define (avg . r) (/ (apply + r) (length r)))
(define (stddev . r) (* (/ (length r) (- (length r) 1)) (sqrt (apply avg (map (lambda (x) (expt (- x (apply avg r)) 2)) r)))))

(define  %time/gc '(3.69 3.70 3.66 3.69))
(values (apply avg %time/gc) (apply stddev %time/gc))
$7 = 3.685
$8 = 0.01999999999999997

(define  %real '(15.066 15.924 15.369 14.889))
(define  %user '(15.149 15.695 15.339 15.066))
(define  %sys  '(0.709 0.836 0.704 0.679))

(values (apply avg %real) (apply stddev %real))
$1 = 15.312000000000001
$2 = 0.5237633053202561

(values (apply avg %user) (apply stddev %user))
$3 = 15.31225
$4 = 0.32283655995634153

(values (apply avg %sys) (apply stddev %sys))
$5 = 0.732
$6 = 0.08148074073737369

while true; do time GUIX_PROFILING=gc ./the-optimised-baseN-guix/bin/guix build -d pigx --no-grafts; done

/gnu/store/jfjfg7dnis7v6947a0rncxdn3y1nz0ad-pigx-0.0.3.drv
Garbage collection statistics:
  heap size:        93.85 MiB
  allocated:        317.83 MiB
  GC times:         18
  time spent in GC: 3.71 seconds (22% of user time)

real	0m17,646s
user	0m16,539s
sys	0m0,705s
/gnu/store/jfjfg7dnis7v6947a0rncxdn3y1nz0ad-pigx-0.0.3.drv
Garbage collection statistics:
  heap size:        93.85 MiB
  allocated:        317.83 MiB
  GC times:         18
  time spent in GC: 3.63 seconds (22% of user time)

real	0m18,733s
user	0m16,698s
sys	0m0,691s
/gnu/store/jfjfg7dnis7v6947a0rncxdn3y1nz0ad-pigx-0.0.3.drv
Garbage collection statistics:
  heap size:        93.85 MiB
  allocated:        317.82 MiB
  GC times:         18
  time spent in GC: 3.72 seconds (24% of user time)

real	0m15,429s
user	0m15,448s
sys	0m0,696s
/gnu/store/jfjfg7dnis7v6947a0rncxdn3y1nz0ad-pigx-0.0.3.drv
Garbage collection statistics:
  heap size:        93.85 MiB
  allocated:        317.82 MiB
  GC times:         18
  time spent in GC: 3.70 seconds (24% of user time)

real	0m15,292s
user	0m15,315s
sys	0m0,635s

(define %time/gc '(3.71 3.63 3.72 3.70))
(define %time/real '(17.646 18.733 15.429 15.292))
(define %time/user '(16.539 16.698 15.448 15.315))
(define %time/sys '(0.705 0.691 0.696 0.635))

(values (apply avg %time/gc) (apply stddev %time/gc))
$17 = 3.6900000000000004
$18 = 0.04714045207910329
(values (apply avg %time/real) (apply stddev %time/real))
$19 = 16.775000000000002
$20 = 1.9554380015172506
(values (apply avg %time/user) (apply stddev %time/user))
$21 = 16.0
$22 = 0.8304360300468671
(values (apply avg %time/sys) (apply stddev %time/sys))
$23 = 0.6817499999999999
$24 = 0.03660449274186007


Tests show neither a decrease nor an increase in timings.
Now looking at the allocation count:

The heap size before:
  heap size:        93.85 MiB
  allocated:        325.20 MiB

The heap size after:
  heap size:        93.85 MiB
  allocated:        317.82 MiB

A small improvement (-2.3%).