Wow, 10 cm would be way to long if that were just the prob which was below the threaded section. Got a picture with a ruler beside it to show us? This is what my thermocouple looks like and it has about 1.75" sticking past the threaded section.
IMO, smoke is not a good indication of your EGT's. My truck doesn't smoke at all, but on a long climb, I can easily reach 1200*F (still with no smoke), so just be careful
