I know it is normal too see the top card hotter than the lower, but at what differential would be considered abnormal? I have 2x GTX 780 Lightning's running in SLI. The fans on them are pretty quiet so I have them running at 75% once they get over 60 degrees. I have just benchmarked them and the bottom card maxed out at 53C and the top 73C, so a 20C differential which is more than I was expecting. Is this high spread due to them not being reference models? They are only around 1 inch apart as well and the bottom one is blowing hot air directly into the top ones fans so I think all of this is compounding and making the top card significantly hotter. Let me know your thoughts.