Filling immiscible polymer blends with carbon nanotubes (CNTs) is a widely used approach to combine the advantages of tailored property design of polymer blends with achieving electrically conductive materials at low CNT loading. Thereby, the concept of double percolation may be used, when the CNT are selectively localized in one continuous component, e.g. in co-continuous blends. In this contribution, polycarbonate (PC) based composites and co-continuous PC / poly(styrene-acrylonitrile) (SAN) blends were filled CNTs by melt mixing in small-scale. Thereby, multiwalled CNTs were premixed in the thermodynamically preferred PC component and for the selectively filled blends subsequently mixed with the SAN. By using two sets of mixing parameters, different states of filler dispersion in the premixtures and in the blends are obtained. With higher mixing speed and longer mixing time better filler dispersion is obtained. However, with increasing CNT dispersion, an increase of the electrical resistivity around the percolation threshold is observed, for the PC-CNT composites as well as (PC+CNT)/SAN blends. This suggests that the higher mixing energy - required for better dispersion - also result in a more severe reduction of the CNT aspect ratio. This effect was proven by CNT length measurements using TEM. Moreover, melt rheological studies showed higher reinforcing effects for composites with worse dispersion. The Eilers equation, developed in 1941 by H. Eilers for filled emulsion describing the melt viscosity as function of filler content, could be used to fit the data and gives information about an apparent aspect ratio change in the PC composites. These data were in accordance with the reduction of CNT length values as measured using TEM. The applied fitting could be also transferred to the blends and serves for a qualitatively based discussion, since again the tendencies were in accordance with CNT length measurements.