I use Rossignol B2's in a 176 length. I'm 5'9" and about 160lbs ... but I have also been skiing for about 28 years although not much on telemarks. I went for the Rossi 'cos they are soft compared to my alpine skis as well as really light and so more forgiving, although not especially stable. They were also on sale, which helps ($350CAD from new)
This was also based on a recommendation from another instructor who telemarks a lot. The advice I got was to go for a length similar to what you would take if getting a pair of all mountain alpine skis.
If you are fairly fit & reasonably aggressive I would probably be opting for around 170cm.