I just watched an ep on new GT-R, 1M and 370Z.
1M was a single review. 370z (the only ep with 370z in it) was up against the new Z4. Which, as you said, Clarkson chose the 370z over the other, but it was against the Z4, not 1M.
1M and Z4 have the same engine though, 1M's one is just boosted up a bit more.