In this paper, we develop a quantitative design technique for multi-walled carbon nanotube (MWCNT) bundle-based interconnect, which we utilize to examine the performance, reliability, and fabrication requirements for future nanotube-based interconnect solutions. Leveraging a MWCNT model that achieves a high degree of accuracy compared to experimental CNT measurements, we develop the first closed-form formulation for the optimal nanotube diameter and nanotube bundle height. The results indicate that the proposed design method decreases delay by 21% and 29% on average compared to non-optimized MWCNT and SWCNT bundles. We find that future CNT bundle fabrication processes must achieve a nanotube area coverage of at least 30% for optimized CNT bundles and 40% for non-optimized CNT bundles to obtain competitive performance compared to copper interconnect. We also find that large diameter MWCNT bundles are significantly more susceptible to process variations than SWCNT bundles, which will have important reliability implications in future nano-scale ICs.