Pairing Field size as security parameter
Thats a bit outdated as for your choice of setting (with $k=6$) the 170 bit will give you 1020 bit security in the subgroup of $F_{q^6}^*$.
In your case for embedding degree 6 I would at least take 224 bits which would give you 1344 bits in the multiplicative subgroup of $F_{q^6}^*$ or you even go to 256 bits which will give you 1536 bits. Anyways the setting with embedding degree 6 will give you not an optimal efficiency-security tradeoff as you have to take far higher security levels in the curve to achieve acceptable security levels in $G_T$.
The choice of Baretto-Naehrig curves will give you the optimum security-efficiency tradeoff (they have $k=12$) today and they are for instance implemented in the RELIC toolkit.
You may look here what parameters for elliptic curves and multiplicative groups of finite fields are recommended today by different institutions.

Update (2021): As mentioned in the comments, already in 2014 the parameters mentioned above for MNT curves only gave security (far) below 100 bit. For an up to date reference on parameters one can look here: https://members.loria.fr/AGuillevic/pairing-friendly-curves/