Despite greasing the new cable and even applying moly on the cable ends (where it enters the tach drive and the tachometer), after 38 miles of use the cable snapped in the exact same place as the broken one that came with the bike - just above where it enters the tach drive
I replaced it with my spare, and this time sprayed teflon throughout the cable sheath to line it with PTFE like BMW does with their cables. We'll see if that helps any, but I'm open to suggestions. I'm going to keep my old cable and maybe put a weld on it, you don't find these things everyday
Also bought a mirror from Moto Guzzino
I'd been running mirror-less since the bike's completion because I couldn't find any bar ends that I liked and also couldn't bring myself to drill into the new Tommaselli controls to mount conventional mirrors. This clamp-on one saved me from all that trouble and is seemingly built pretty well. We'll see how it turns out. I really didn't think I'd need a mirror, but honestly I get nervous at stop signs and traffic lights without one - I'd like at least a warning when someone is going to slam into the back of me.