hyperthreaded i386:

vanilla build, -j2 [make all unit_tests tester]
real    24m11.690s
user    46m16.334s
sys     1m27.913s

p-t build, -j2 [make all unit_tester tester]
real    13m23.987s
user    24m23.935s
sys     0m50.639s

vanilla check
real    21m34.890s
user    16m15.537s
sys     1m24.701s

p-t check, -j1
real    20m41.652s
user    16m31.090s
sys     1m26.921s

p-t check, -j2
real    14m55.986s
user    22m34.057s
sys     1m49.027s

p-t check, -j3
real    14m9.986s
user    24m27.144s
sys     1m54.955s

----
quad amd64:

vanilla build, -j4  
real    3m17.451s
user    11m32.287s
sys     0m51.611s

parallel-tests build, -j4
real    2m41.438s
user    9m50.505s
sys     0m44.987s

vanilla check
real    12m11.844s
user    7m32.572s
sys     0m49.575s

p-t check, -j1
real    10m42.816s
user    7m30.656s
sys     0m39.698s

p-t check, -j2
real    5m14.981s
user    7m12.891s
sys     0m35.722s

p-t check, -j3
real    3m51.695s
user    7m22.528s
sys     0m38.858s

p-t check, -j4
real    3m32.917s
user    7m28.820s
sys     0m38.374s

p-t check, -j5
real    3m36.815s
user    7m29.852s
sys     0m40.111s