Joey, I am away from home right now in Toronto on a commercial job and thus away from my tables, resources and slide rule. But off the top of my head:
80W load on 100' of 12/2 cable = 1.0 Volts Drop giving 11volts at the LAST fixture in that scenario. Certainly above the lower limit threshold of 10.75 volts to maintaim lumen output and colour accuracy of a 12v lamp. Its not perfect, but clearly "do-able"
(Total watts on Cable x Length of run in feet / Cable Size Constant (7500 for 12/2) = VD
I have always preferred to run my lamps at between 11.2 and 11.7 volts. The output is still very good and the extra lamp life helpful.
Gregg, do you have your handy dandy NS Voltage Drop Slide Rule handy? Care to chime in?