Found the following reference, which explains the different spectra between WR120 (WC7) and WR 11 (WC8)
C
iii 5696 emission is very sensitive to
mass-loss rate, so weak winds for LMC WC stars would produce negligible Ciii
5696 emission (WC4 subtypes) and strong winds interior to the Solar circle
would produce strong Ciii 5696 emission (WC8-9 subtypes)
See
http://arxiv.org/PS_cache/astro-ph/p.../0610356v2.pdf
for more detail!!