I keep mine about 79.5 (since I added a fan). Everything that I have read pegs natural reef conditions warmer...82-83. However, there are some downsides to the warmer temps. Most of the explanations make me dizzy but they center around oxygen holding capacity and ph/alkalinity. If you have a power outage, lower temp is usually accompanied by higher dissolved oxygen content that will help your tank survive longer without oxygenation and power.
IMO, 74 is too low and 78 should be fine. Keep in mind that smaller tanks are subject to more rapid fluctuations in temp (and everything else).